Developing the Sandbox: Rumor Tables

This post is part of my series on developing the sandbox. You can read other posts in the series here. The series will, when necessary, go into detail on the development of my sandbox for Dungeon Module B1: In Search of the Unknown, but will also discuss sandbox development more generally. You can read play reports from my B1 campaign here.

This post will focus on creating rumor tables for your towns and cities. 

What is the purpose of an in-world rumor in a TTRPG? According to the Designing Dungeons course (which is of course preoccupied with dungeons specifically), rumors provide clues to the dungeon, reinforce its themes, and point the players back towards elements of the dungeon they may have missed. More broadly speaking, in a sandbox setting, rumors drive investigation and exploration of the world and help make the world feel more lifelike.

In short, rumors are information. Information allows the players to make choices - as always, the better the information, the better the player's ability to anticipate their choice's impact. Thus, we need to make sure our rumors provide good information.

What about false rumors? That's a thing in Dungeons & Dragons, right? False rumors are, at times, delightful. I'm as big a fan of "Bree-yark" is goblin for "We surrender!" as the next guy but, more often, false rumors are just kind of detrimental to play. As Gus L. points out, they waste time and erode trust  between players and the DM. They serve a purpose opposite to what rumors are meant to accomplish, muddying themes, sending the players on wild goose chases, or paralyzing them entirely.

Since I am currently running my B1 sandbox, let's look at B1's rumor table as an example (as an aside, see this post about B1, Caverns of Thracia, and the hunt for the first rumor table.):

This is not a bad rumor table. It tells the players what sorts of monsters might be found in Quasqueton, that it has multiple levels, that there are secrets within, and what sorts of rooms the players might expect to find there. The information is somewhat pedestrian, but this is an introductory module. The rumors are not only telling the players what to expect from the dungeon, but what to expect from the game itself. 

The false rumors, however, are largely terrible.

Zelligar does have a workshop in the stronghold, but the rumor is "false" because he didn't work on magic stronger than any known to man (he just used it to torture barbarians, stocked it with containers full of mundane junk, and kept a ghost cat in a jar to troll adventurers). There is no 100,000 g.p. gem hidden in the stronghold. There is no curse upon the place or its treasure. The "treasure" hidden in a pool of water is a totally pointless illusion. The dungeon is not filled with guards, and Rogahn and Zelligar have not returned.

While there are kernels of truth to some of these rumors, more of them either set up the players for disappointment or actively discourage them from going to the dungeon - you know, the single adventure site upon which the entire module depends. What happens when the players comb the whole place and don't find any sign of magic "stronger than any known to man" or of a 100,000 g.p. gem? What happens if they decide the dungeon sounds too dangerous? It's full of guards, and Rogahn and Zelligar have come back, too. It's treasures are all cursed anyway, so what's the point?

"But wait," you might say, "you talk all the time on this blog about running AD&D the Gygaxian way, with constant taxes and annoying NPCs who hate the player characters and want them to go away and die. This adversarial bullshit should be right up your alley!"

And you are kind of right. I am trying to run my game in some approximation of that style, and I do find it quite fun. For some reason, I draw the line at false rumors. Why? I don't know. I think I just have a lot of information about this setting that I want to communicate to the players, and I don't want to waste space on my tables with four different (false) rumors about how the dungeon is dangerous. The players know the dungeon is dangerous. What actually makes it dangerous?

That's not to say I'll come right out and tell the players that the magic stone in Quasqueton has a 5% chance of granting a limited wish specifically. Unreliable rumors are good! "An enchanted stone within the stronghold will grant a wish to anyone who chips off a piece of it and places it within their mouth" is a false rumor because the stone does other things besides granting wishes, but the fact that it grants wishes is true. The rumor itself is a bit too on the nose for me, but that's besides the point.

Now, in a sandbox, I don't want all my rumors to be about the dungeon. I want my rumors to also point to other settlements, strongholds, and monster lairs. I want them to give hints about outdoor encounters. I want them to indicate what sort of monsters prowl the town's streets and to clue the players into the political landscape of the settlement or what events I have scheduled on my campaign calendar.

How do you create a rumor table? These posts each have a sort of "generic" rumor table you can roll on almost like a spark table to create more specific rumors. This is neat! I personally don't need this tech, but you might find it useful if you're having a hard time coming up with ideas.

What I've done recently is split my rumor table into three tables. How do I structure that? I will give you a hint - the three tables are derived from this page of the AD&D DMG:

I don't think it's particularly hard to figure out, so I will tell you. Much like modern D&D puts forward three "pillars of play" (combat, exploration, and social interaction), here I think Gygax is putting forward a different (parallel) set of three pillars - dungeon expeditions, outdoor exploration, and town adventures. Thus, my three rumor tables list dungeon rumors, wilderness rumors, and settlement rumors.

"Wilderness rumors" is a bit of a misnomer. Just as the "exploration" pillar is more like the "everything else" pillar in modern D&D, "wilderness/outdoors" is the "everything else" of the sandbox. This includes rumors about other settlements, strongholds, monster lairs, and outdoor encounters. The town and dungeon are both complex enough environments to warrant their own tables, but the other locations in the sandbox really just need one rumor to point the players in that direction (or, in the case of outdoor encounters, give them fair warning).

While dungeon rumors will be hyper-specific, providing information about specific rooms, monsters, tricks, traps, treasure, and other secrets, all other rumors can be somewhat vague - again, just kind of nudging the players that way. Dungeon exploration is the default mode of play in the early game. In most cases the players will not need to be directed towards the dungeon, but they will need specific information about its contents. As the campaign evolves, however, you'll want them to slowly become aware of adventuring opportunities in the town/city and elsewhere.

For my dungeon table, I included those rumors from B1 which I liked, then supplemented them with my own. I basically combed through my version of B1 and thought of every bit of information I might give to the players about the place - again, rooms, monsters, tricks, traps, treasure, and other secrets. These are very broad, and complement each other when combined. Some rumors might simply say "There are goblins in Quasqueton" or "There are orcs in Quasqueton", while others might be more specific: "The goblins and the orcs of Quasqueton hate each other", "The orcs of Quasqueton worship a magic stone" or "The orcs of Quasqueton are at war with one another."

For my town rumor table, I generated one rumor for each element of the town which I wanted to put on the players' radar - that is, its locations, NPCs, and potential encounters. There's a rumor about the wizard who rules the town, a rumor about the lesser wizard who serves him, and a rumor about the cleric who rules her own stronghold. There's a rumor about beasts attacking people, a rumor about spirits haunting the streets, a rumor about a corrupt official blackmailing merchants, and a rumor about a derelict house from which strange lights are seen at night. All of these point to locations or warn the party of potential encounters. I also include a permanent entry on the table for whatever town event is coming up on my calendar.

Likewise, my wilderness rumor table has one rumor for each "wilderness" location, plus a few more for particularly noteworthy outdoor encounters which aren't otherwise covered by my other locations. Brigands terrorizing the countryside would be covered by the rumor about the brigands' stronghold, and owlbears in the forest would be covered by the rumor about their lair - I would not include an additional rumor for those outdoor encounters just because they also appear on my encounter tables. If there are unique or interesting monsters wandering the wilderness who otherwise don't have their own lairs (fey "river women" who don't live anywhere in particular but are sometimes encountered deep in the forest), those get their own entry on the table.

Since I replace outdoor encounters on my tables once they've been used, I update my rumor tables accordingly. You may not have to do this, but I do think a rumor table should be a living document, assuming that the status quo is changing even when the player characters are being somewhat inactive. 

This goes for rumors about the town and dungeon as well. If the first rumor discloses that the wizard and the cleric in town have an uneasy truce, then the next might disclose that the cleric has attempted to assassinate the wizard. If the players already have the rumor about the orcs in the dungeon being at war, the next rumor might tell them that one side has triumphed over the other.

You can go down a real rabbit hole with this stuff, creating subtables for each entry on the main table (you could have a d4 table of rumors about the wizard overlord or the plundering brigands specifically), but I think this is overkill. The rumor just makes the players aware of the thing. If they want more information, they can start asking specific questions, and I have most of the information to answer those questions, if appropriate, as needed. No need to make your rumor tables maddeningly comprehensive.

With three separate rumor tables covering distinct topics, when players go hunting for rumors, I can ask them: Do you want rumors about the dungeon, the town, or the wilderness? I view rumor-gathering as an active pursuit, not a passive one. The players don't just accumulate rumors by existing in town. The players have to say they want to do it, and they have to spend time and money doing it, just like with almost anything else they do in town. Since they are choosing to gather rumors, it also makes sense to me that they be able to choose which rumors they're looking for.

I like this rule of thumb for rumor-gathering from OD&D:

Delta's post on the subject clarifies that this was likely intended as a means for players to find out about expeditions by rival players operating in the same campaign simultaneously, but I see no reason why it can't apply more broadly. I feel there has to be some cost to gathering rumors, and, as Delta points out, this is seemingly the only guidance provided in any edition of D&D. It is a little bit cost prohibitive for player characters just starting out, but that's okay with me. They can either spend less on equipment and get some information instead, or they can go in blind for their first expedition.

It's also worth considering how you choose to present rumors to the players. Do you attribute each rumor to a specific NPC? Personally, I'm fine with abstracting it. I have enough NPCs to worry about as it is, and I can kind of wing it when it comes to where a rumor is coming from based on the nature of the rumor and where the players hear it.

Do you roleplay out the dispensation of rumors? I don't know, do you roleplay shopping? Again, I'm perfectly fine with abstracting this and simply telling the players what they hear. I don't need to tell it to them in a gruff sailor's voice. If they start asking follow up questions, maybe, but I'm only going to spend a significant amount of game time on this of the players decide that it's worth their time.

I also like this post about tying rumors to settlement events, however, again, I think it might not be for me. I have a separate procedure for determining when events happen, and events already provide information about what's going on in the world. It makes sense to me that players should be able to learn about something that's going to happen before it happens. That is, the players should be able to learn that loggers have spotted kobolds in the woods before the kobolds launch a raid on the town.

There's even more to explore. Player characters may have the choice to live at different economic levels and in different conditions. The character who is unwashed and flea-ridden and sleeps in stables does not have access to the upper classes, and the haughty character who dresses in fine silks and gold rings might be shunned by the downtrodden and class-conscious folk. Their affiliations may likewise affect their access to rumors. A paladin will not have access to criminal networks, and a thief may not be privy to the church's scuttlebutt.

What rumors are exchanged by loggers and hunters? How about dockworkers and fishermen? Merchants and officials? Mages at the Wizard's Day ball? Do monsters know rumors? Can you gather rumors in the dungeon?

You can clearly get deep in the weeds with this stuff. For now, I prefer to keep it simple. If you were out drinking at the tavern and heard tell of some cool new rumor tech, I have 10-60 gold pieces with your name on them!

Developing the Sandbox: The Campaign Calendar

This post is part of my series on developing the sandbox. You can read other posts in the series here. The series will, when necessary, go into detail on the development of my sandbox for Dungeon Module B1: In Search of the Unknown, but will also discuss sandbox development more generally. You can read play reports from my B1 campaign here.

A man of disputable wisdom once said that "YOU CAN NOT HAVE A MEANINGFUL CAMPAIGN IF STRICT TIME RECORDS ARE NOT KEPT." This has since become a bit of a meme in the TTRPG community. It is an emphatic declarative statement written in all caps by a larger than life figure in the hobby whom a lot of people enjoy ridiculing, often for good reason. But is there truth to it?

Kinda! Honestly, I've actually never kept a calendar for any of my D&D games. They still felt pretty meaningful to me. Nonetheless, at the end of my longest-running campaign ever (a three and a half year 5e game that took the player characters from 3rd to 20th level and beyond), I felt myself regretting not having a calendar. 

How long had it taken for the characters to make their ascent to power? How long had they known each other? When did they first meet that henchman? How many seasons, moon's turns, and holidays had passed them by? I didn't know.

I was running the campaign by the seat of my pants. I randomized the weather every day. It was an NPC's birthday or the day of some festival when I needed it to be. If a PC became a lycanthrope, only then would I bother to figure out when the next full moon was. Dungeons were restocked, new monsters moved into the region, and factions moved against one another and towards their goals when I felt like they should.

It worked for me. I didn't need a calendar, but I felt myself wanting one all the same.

One of the benefits of running a small sandbox (like the one I created for B1) is that you stand a reasonable chance of, at some point (possibly even before play begins), actually finishing prepping the whole thing for play. Technically this is possible for larger sandboxes as well, but it's a more Herculean task, and you are more likely to burn out before play even begins or to fall behind during play (if, like me, your interest waxes and wanes naturally as the campaign goes on), likely resulting in a lesser quality experience for you and your players.

The sandbox is never actually finished, because running the sandbox is its own thing that requires maintenance between sessions. The benefit of having most of your sandbox prepped and ready to go is that you have more time between sessions for those more ancillary pursuits. When you're not rushing to detail the owlbear den the players intend to clear out on their next expedition, you can instead spend that time restocking the dungeon, updating your outdoor encounter tables, and figuring out if those NPCs succeeded in their most recent scheme.

This is also a great time to work on your calendar. Now, the calendar might be one of those things you want to have prepared ahead of play. Perhaps you want to generate a month's worth of weather. That's pretty reasonable. But I've run nearly two dozen sessions of my B1 campaign, and I'm only just now feeling the need to create one of these bad boys.

What made me want a campaign calendar? Well, part of it was that I just thought it would be neat. That's reason enough. Part of it was remembering the regret I felt at the end of past campaigns. A big part of it was that the party started to accumulate an absurd number of NPC hirelings and paid them in advance, and the way that I was tracking the length of their employment was totally impractical. 

So, I made a calendar.

If you like, you can go on rootring and search "calendar", read all the advice, and come up with something that works for you. Like making a dungeon, there is tons of advice on this subject, and it's impossible to summarize without conducting a meta analysis.

Here's what I did. I got a calendar template from Google Sheets (I used the first option, which is just a sheet for each month of the year and a cell for each day of the month). This is a 2026 Earth calendar. There are no fancy names for the months of the year or the days of the week. You can do this if you want, but it isn't important to me, so I didn't do it for now (I remember really liking the vanilla fantasy names for the month presented by Shamus Young on his Twenty Sided blog...21 years ago?!).

First, I went back through my play reports and figured out when the campaign began. I had already decided that the campaign began in Spring, because that seemed like a reasonable time when adventurers would embark on adventuring activities. For simplicity, Spring is March, April, and May, Summer is June, July, and August, Fall is September, October, and November, and Winter is December, January, and February (this will be important when determining the weather).

I looked at when my first session took place in real life - March 12th. Perfect! I decided that was the in-game start of the campaign as well. Then, I went through my play reports, looking for any mention of the party resting or time passing. I also noted when the party brought on their hirelings and for how long. I ended up with this:

After 20 sessions and 6 months of play, just 13 days had passed in game. Wow! You could go more in depth, noting which sessions occurred during which days and what specific activities the party engaged in - and I might do that still - but it felt unnecessary at the moment.

Since one of the main reasons I wished to start work on the calendar was to track the length of NPCs' employment, I went into the future on the calendar and marked the days when each hirelings' employment would expire. At this rate, it will be another 5 or 6 sessions before the party's porters' and mercenaries' contracts need to be renewed, and 18 or 19 sessions before the crew of the party's river barge can retire, but it's useful information to know. Time passes weirdly during a campaign. A single day might be several sessions, and the next session might cover several days.

I also liked the idea of pre-rolling weather for a month or so. In the real world, you can often tell when it's likely to rain in the coming days, and I want to be able to foreshadow that (the players might not want to embark from town if it seems like they're going to get a torrential rainstorm the next day). It also allows me to skip rolling for weather at the table, and makes me less likely to forget to do so. So, I rolled weather for the rest of the month (as well as the following month, since we're nearing the end of the current one).

I used these hex flowers to determine the weather:

I like these because they're evocative, they only require a single roll for each day, they're based on the seasons, and each day's weather affects the next day's weather. Depending on your system of choice and how weather mechanically impacts things like overland travel or encounter chances, you'll likely have to do some interpretation of the results, but it works reasonably well. In addition to marking daily weather on my calendar, I noted if the weather imposed penalties on overland movement or modified outdoor encounter chances for that day.

Since I am using a real-world calendar, I could also look up what the weather was actually like on each day in some area of the real world comparable to my setting, but in practice I found the information I was looking for too difficult to find, and the information I did find too fiddly for my uses. It would be fun to use a system where the weather can change throughout the day, as it does in real life, but I personally don't need that.

Another thing I thought would be fun and necessary to track is the phases of the moon. This information can be based on the real world and is pretty easy to find, but you can also just make it up. Pick a day during your first month that the moon is full, then have it be full again every 29 days or whatever. Or decide that full moons in your setting are more or less common if you like. You'll have to come up with that yourself. You can also track other celestial events like eclipses and supermoons the same way.

Why is the moon important? Well, don't tell my players, but my sandbox has lycanthropes in it. I want to know when there's increased lycanthrope activity. The player characters might in turn become lycanthropes, and I want to know when they're going to transform and wreak havoc, or do whatever it is werebears do (for example). The AD&D DMG has this whole table breaking down the percentage chance of a cursed individual transforming into a werebeast based on the current phase of the moon:

Clearly you will need to accurately track the phases of the moon to use this thing properly! Also note that you will need to know for how long the character has been a lycanthrope. Another win for the campaign calendar!

You might also decide that the local Evil temple does some nefarious stuff during the lunar eclipse or that magic is more powerful during that time. That seems like a fun application of this tech.

Another fun thing you can do with your calendar is track settlement events like holidays, festivals, NPC birthdays, or whatever. If the players plan for their characters to spend a week in town, it would be nice if they knew that it was the friendly wizard NPC's birthday so that they can arrange to get her a gift. If they're planning to venture out into the wilderness but they learn that tomorrow is the annual Cheesemonger Parade, they might decide to stick around an extra day to attend the festivities and rub elbows with important contacts in the cheese industry.

I roll a d20 for each day on my calendar, and a result of 18+ is some day of significance in the settlement. I like this table from the 2014 5e DMG:

This is one of the many unsung tables of that oft-maligned book, which is honestly full of useful little stuff like this. You'll have to ignore some stuff - seasonal events like equinoxes and solstices, midsummer/winter festivals, fertility/harvest festivals, and celestial events which you're already tracking by other means - but overall this is pretty good stuff!

I wouldn't bother determining events like this for every settlement in the sandbox. I simply rolled for the largest settlement - the one the PCs are most likely to spend extended amounts of time in. You can probably safely assume that the villages, hamlets, and thorps which surround your town celebrate more or less the same events as the town itself.

There's also no reason to limit this to settlements only. Do the denizens of the dungeon celebrate holidays? Is there some mutually recognized armistice day where they come together and parade through the dungeon? Do monsters in their lairs celebrate birthdays? Is a tournament being held at the fighter's stronghold?

You might also want larger events going on in the background - wars and famines and natural disasters and stuff. Joel at Silverarm Press wrote a post which highlights a neat table from uh...Oriental Adventures, on which you can roll for a single yearly event which in turn influences which monthly events are likely to occur. This is pretty neat tech. I haven't tried it out yet, but it's worth a look if you want like, a war happening somewhere "off screen" (or maybe even on it). Warren D. of I Cast Light! also reworked the table on his blog.

Just as you might do with weather or the phases of the moon, you can also pull yearly/monthly events from real life. Simply pick a real-world year that corresponds roughly to the period during which your campaign takes place, Google it, and look at the Wikipedia article to see what happened that year.

The calendar is also useful for tracking faction events. I know that the wizard that rules my town has a tenuous truce with the cleric who rules her own stronghold. The wizard also has a mutually friendly working relationship with a subordinate wizard who wishes to build a stronghold of her own. The cleric wants to kill the subordinate wizard. Will the cleric achieve her goals? Will the truce deteriorate? When does that happen? You will probably want some way of running factions.

You might also use the calendar as a simple timer. One of my biggest bugbears in adventure design is when some time-limited event is happening in the setting (a monster is growing in power, a city is being overrun with plague, or a bad guy is working on a nasty ritual), and the conditions of those ongoing events don't change unless the player characters intervene somehow. 

There's something to be said of a "powder keg" scenario where everything exists in a tenuous equilibrium, requiring some "X factor" (the player characters) to move things decisively in one direction or another, but that doesn't mean everything has to remain static. If some event is going to occur if given enough time to gestate, you should track it somehow. No more Big Bad Evil Guys waiting until the player characters show up to complete their rituals!

There's a party of adventurers camped out in the wilderness, clearing land to build their stronghold. When do they finish? The wizard in town is plotting against them, trying to recruit a band of ogres to root them out. When does he get the ogres to act? There are brigands who have usurped a stronghold and keep its rightful ruler prisoner. When do they execute her? Set dates for all of these things on your calendar. If the player characters take actions to aid or thwart these plots, adjust the timeline on your calendar.

These are the broad strokes. The campaign calendar is of near infinite utility, and there are many things both big and small which it can be used to keep track of. Here are some examples of what else you might track:

• When does a disease or parasitic infestation run its course or kill the afflicted?
• When do followers arrive at a player character's newly built stronghold?
• When does an NPC spy complete a mission and, if the mission fails, when can the characters safely employ another spy on the same mission?
• When does a slow poison kill?
• When does a character or NPC finish crafting an item (magical or otherwise)?
• When does a sage find the answer to a question (or discover that the question is unanswerable) and when can another question be asked of the sage? When does the sage finish acquiring a new minor or major field of study?
• When do henchmen respond to recruitment attempts?
• When does an unfaithful cleric finish atoning for their sins?
• When must an Evil cleric reassert control over their undead minions?
• When does an injured player character make a full recovery?
• When do effects like psionically induced comas, magical enchantments, or temporary insanities end?
• When does a character who mixed an oil of slipperiness with an oil of etherealness return from being lost in the Ethereal Plane? 
• When is a soul no longer trapped in an amulet of life protection, when does a character finish reading a manual of bodily health, and when can a character again invoke the Goat of Terror, and other magical item effects?
• When does an assassin finish their study of poisons?
• When does a character finish their training and level up?
• When is construction of a font or basin for holy water completed?
• When is spell research completed?
• When does an Evil artifact inflict its malevolent effects upon its possessor?
• When has a character known a hireling or henchman long enough to warrant a loyalty score increase?
• When does a character finish training a griffon as a mount and when do they finish training to fire a bow from its back?
• When does the next peasant rebellion occur? When does the rebellion evolve into a civil war?
• When do the characters have to pay taxes?
• When does a cleric or magic-user finish creating a golem?
• When is a paladin's warhorse or a conjured demon released from service?
• When is construction of a stronghold (and mazelike dungeons thereunder) completed?
• When does a character die of old age?

(This list was created by combing through the AD&D DMG with Ctrl+F, keywords "days", "weeks", "months", and "years". There are undoubtedly a great number of many other things you can track as well!)

The calendar is not just for the DM's benefit. Just as players can master a dungeon's layout and use their knowledge of such to plan optimal routes for exploration, treasure extraction, and avoidance or ambushing monsters, they can master the calendar and use it to their benefit. If the DM knows when it will rain, when the hirelings' contracts expire, and when the NPC's birthday is, this should be telegraphed to the players in some way so that they can make informed choices.

Do they wait another day in town to let the weather pass? Do they prioritize their next expedition, before their hirelings demand more money? Do they make sure to be back in town so they can attend the wizard's birthday? There's a full moon tomorrow night. Should they plan to patrol the streets of town and lay a trap for the werewolf? When are the owlbears out hunting versus sleeping in their lair? What can they do before the royal ball to improve their chances of getting an invite?

These are all more or less things you will have to track as a result of player actions - they are less about developing the sandbox than they are about running it. You can wait until your game is underway and until you absolutely need the calendar before creating it (as, admittedly, I did), but hopefully I have demonstrated why creating the calendar upfront can be beneficial as well.

Developing the Sandbox: Strongholds

This post is part of my series on developing the sandbox. You can read other posts in the series here. The series will, when necessary, go into detail on the development of my sandbox for Dungeon Module B1: In Search of the Unknown, but will also discuss sandbox development more generally. You can read play reports from my B1 campaign here.

In this post, I'll discuss the development of those strongholds in your sandbox which are ruled by NPCs. These are your classic fighters' bastions, wizards' towers, clerics' temple fortresses, and thieves' dens and hideouts, but it doesn't stop there. 

Paladins will rule strongholds somewhere between that of a fighter and a cleric. Rangers may rule fortified compounds in a more wilderness locale. Illusionists will disguise their strongholds to appear mightier than they truly are, or as simple earthen mounds or other natural features. Druids will rule secure woodland groves. Monks build monasteries. Assassins rule imposing wilderness fortresses.

Monster lairs can also be strongholds, and many famous "monster lair" modules play very similarly to strongholds. Bandits, berserkers, brigands, and dervishes may come to inhabit them. Giants and many underwater creatures will build strongholds as well. 

Two things that this post will not cover are (1) strongholds built by the player characters and (2) deserted strongholds, which are likely naught but ruins on the surface and which fall more readily into the dungeon category.

Most scholarship (i.e. blogs) on the subject of strongholds in D&D pertains to those built by player characters and the rules for doing so. I'm instead interested in how to design and key an existing NPC stronghold for the players to interact with. 

Strongholds are kind of like dungeons in the sense that the player characters can move from room to room and interact with objects inside. They will contain "empty" rooms, "monsters", traps, and treasure. They are also kind of like monster lairs in that they are home to a type of "monster" - broadly speaking, most often men and/or demi-humans, but more specifically, powerful NPCs that are very much like the player characters themselves, plus their henchmen, men-at-arms, special followers, pets, and the like.

Strongholds are tricky because they are very much real places, and complex ones at that. You'll want to have some knowledge about different types of real-world strongholds and how they functioned. You have to think about how real-world strongholds were constructed and defended, and anticipate ways in which your players might want to infiltrate or lay siege to them. You have to think about who all lives there and how much room is needed to house them.

Dungeons are similarly complex, but they're not exactly real places. It might be hard to imagine them without something historical to reference, but there are often robust procedures for designing them, and lots of advice on blogs. Because they're not really real, you can also let your imagination run wild. 

Monster lairs are "real" in the sense that bears and wolves and the like are a sort of "monster" that lives in our own world, and you can somewhat easily imagine what such a place would be like if instead an owlbear lived there, or what an otherwise normal cottage would be like if a leprechaun were instead its resident. They're also not usually especially complex, so there isn't a huge cognitive load when designing them.

There are also more fantastic elements to consider. What spells are laid upon the stronghold? Are there any monstrous inhabitants kept as pets - perhaps a subdued dragon or some enslaved monsters? Perhaps it's a stronghold like in OD&D, with heroes riding griffons and rocs, or defended by chimeras, trolls, manticores, and the like:

Just as you might steal some dungeons for your sandbox to lighten your workload, you can steal strongholds too. You can pretty easily steal the Keep on the Borderlands, Castle Ravenloft, the Hall of the Fire Giant King, or whatever. But you can't always steal exactly what you need, and you might want to create something original. It's not much fun to just use the Keep on the Borderlands over and over again. Is there a good adventure out there which features a fortified druid's grove? I don't know. I'll probably have to make one.

Because they are complex locations, inaccessible by design, ruled by powerful NPCs, and inhabited by large numbers of potentially hostile defenders, I generally assume that NPC strongholds will be one of the last places which the player characters explore in depth. Thus, they usually wind up at the very end of my list of sandbox locations to develop in more detail.

As with every location in my sandbox, before I go into more detail, I start with a minimalist sketch. For strongholds, this includes the stronghold type, who rules it, and how the ruler and their followers might react upon first meeting the player characters, as well as how they relate to those locations which surround them.

For the type of stronghold, I use this handy table from the AD&D DMG:

(Spoiler: The section on CONSTRUCTION AND SIEGE ENGINES really doesn't provide any details about castle types aside from how long it takes to build them. There's lot of information about excavation and mining - including notes on the efficiency of slave labor - a sort of glossary of castle features and how much each costs, and some rules for sieges. This section is kind of interesting, and the glossary is worth looking at, but it won't help you too much in actually designing such a location for your game.)

A castle can be totally deserted, deserted and inhabited by a monster, inhabited by humans (that is, bandits, brigands, berserkers, or dervishes), or inhabited by character-type NPCs:

Both types of deserted castles fall into the dungeon bucket, so we'll focus on just the other two types. There's another table for determining the type of humans in the castle:

In the case of character-types, it isn't as simple, because in AD&D, the stronghold ruler's class will also have some effect on what type of castle can be built. For example, a thief can only rule a small stronghold in or near a town or city, a monk can only rule a moat house or friary, and a druid's stronghold must be in the wilderness. This means that depending on which class is rolled as the ruler, we might be limited in which type of castle is possible.

I wrote up a handy summary of which type of character can rule a stronghold at what level and what type of stronghold they can rule, which is worth checking out. If you're not using AD&D, it isn't super important, but I think it's at least illuminating, and you can always use AD&D's tables for worldbuilding, even if you're using a different system.

Because the ruler's class affects what type of stronghold can be built and where, I determine that first using this table:

The level column is not quite accurate, which I elaborate on in the aforementioned post on the subject. 

In AD&D, only certain races can attain a high enough level in their class to build a stronghold. For example, only human clerics can reach a high enough level to build a stronghold, so if I roll cleric, I know my ruler is human. 

Similarly, if my stronghold is in the wilderness, I know it can't be ruled by a thief. If I roll monk, I know it must be a moat house or friary, and so on. It's a lot to wrap your head around, which is why I thought it worthwhile to summarize in that earlier post.

Knowing who my ruler is, I can then determine their alignment. This is also dependent upon class, such that paladins will always be Lawful Good, rangers always Good, druids always Neutral, and so on. This then modifies their reaction rolls pertaining to the player characters and their neighbors in the sandbox. 

Using my B1 sandbox as an example, I know that the brigands ruling Fayette's Hold are unfriendly towards Timbershore. They're not hostile, so they aren't attacking the town or riding around the countryside killing people, but they've occupied Ebongrove, the thorp at the foot of the castle and just outside of town, and are demanding tribute from Lambrecht, the wizard who rules his own stronghold in town. I also know that the brigands were originally recruited by Lambrecht to subvert the castle's rightful ruler, and that they're now holding the ruler for ransom. The people of Ebongrove are hoping someone will free Fayette from her cell. Lambrecht is attempting to court the ogres of Okorg's Den to aid him in retaking the castle.

That's pretty much all I need for a first draft for my sandbox. To get this location ready for play, I have to go deeper, starting with who all lives there.

In the case of bandits, berserkers, brigands, and dervishes, I simply use the numbers in the Monster Manual. For character-type NPCs, it will be more complicated:

1d4+1 henchmen, light and heavy cavalry led by fighters, and any additional special followers appropriate for the class. (If I'm interpreting this correctly, a cleric's stronghold is instead garrisoned by their special followers, while the other classes get both their special followers and the garrison listed above? Unclear.) 

The classes of henchmen are determined on a separate table than that used to determine who rules the stronghold:

This table yields slightly fewer clerics, fighters, magic-users, illusionists, assassins, and monks, and more druids, paladins, rangers, and thieves. I will ensure that henchmen are compatible with their masters, so a Lawful Good ruler will not have Chaotic Evil henchmen and a paladin will not have a henchman assassin. The level of these henchmen is determined by the level of the ruler:

If my hypothetical stronghold ruler is a Neutral Good 9th level human cleric, each of their henchmen will be 6th level, and none will be Evil. I find it fun to turn these henchmen into their own little "factions" of a sort, making opposed reaction rules with the ruler to determine whether they're favored, neglected, or on the outs, if they're fanatically loyal, unhappy, or actively seeking to betray their master. Remember that henchmen are, at the beginning, the pitiable wretches of the AD&D world, so it isn't hard to believe they might turn their cloaks if they think they might receive better treatment elsewhere.

A good example of this can be found in my Hexmas sandbox, the Jinglebell Barrens. The Tower of Noel is ruled by a fighter with several henchmen, each with their own personalities and agendas.

A stronghold's garrison will have a mix of from 38 to 64 men-at-arms (average 51). I don't love that this is unaffected by the size of the stronghold, so I like to roll as normal for a medium stronghold, roll twice for a small stronghold and keep the lower roll, and roll twice for a large stronghold and keep the higher roll. So a tower will have 2d4(keep lowest)+8 heavy cavalry, a large shell keep will have d4+8 as normal, and a fortress complex will have 2d4(keep highest)+8.

On to special followers. Clerics get a mix of cavalry and infantry:

Fighters get a medium level leader type and a company of either heavy infantry, crossbowmen, cavalry, or a mix of light cavalry and infantry:

Rangers are awesome and get 2d12 followers of mixed types:

This will mostly be normal stuff like character-type humans and demi-humans, but the lower you roll on 2d12, the more likely you are to get really cool stuff like giant animals, monsters, fey creatures, dragons, giants, treants, and lycanthropes:

This is the only thing in AD&D that really hints at OD&D's table of weird stronghold defenders, and that's too bad. There's no reason that your fighter's stronghold can't be garrisoned by griffon riders or your cleric's temple haunted by undead, but it would be a lot cooler if it was made explicit in some of these tables. Still it is really sick that if you play a ranger you have a chance of a dragon or giant just showing up to your stronghold to hang out.

Anyway, thieves get 4d6 thieves of 1st to 7th level and assassins (upon usurping the reigning Guildmaster/mistress) get 7d4 assassins of 1st to 8th level, 75% of which desert during the overthrow and are replaced by new 1st level recruits. There are more tables for those but they're not really worth sharing following those cool ranger tables.

After all that, you have to do the actual designing of the place, including layout and keying. Since strongholds are real historical places, you can do some research into each kind to figure out what exactly you're creating. You probably know what a tower is, but you might want to look up what exactly is a moat house or a shell keep or a concentric castle. 

Since medieval strongholds are not one of my special interests, I did some research. YouTube has a lot of videos describing different types of medieval strongholds, some with 3D renderings/walkthroughs detailing what might be found inside. I also watched some videos about how various defenses worked and how attackers usually laid siege to such places. I found it all enlightening and super interesting, and it's gotten my gears turning thinking about how I'd handle these scenarios in a D&D game.

The stronghold's character should be informed by the ruler of the stronghold. A thief's stronghold will be filled with nefarious traps. A magic-user's or cleric's will be warded by magic and protected by certain conjured beings. An illusionist's stronghold will be a very frustrating place indeed.

It's good to look over the list of spells available to the ruler and their henchmen to determine what sorts of magical effects might pervade the place, with a special eye towards those with a permanent duration. The stronghold may be guarded by animated dead. It may be lit entirely by continual light spells. Certain areas may be trapped with a glyph of warding. The stronghold may be surrounded by an overgrown thicket affected by plant growth. Locked doors may be affected by Leomund's trap. Other doors may be secured with wizard lock or affected by fire trap. A wall of iron may enclose the stronghold in place of wood or stone walls. Earthworks may be formed by move earth. An antipathy spell may repel attackers from a certain area. Clone vats may be found in one chamber. The windows of the ruler's chambers may be reinforced by glassteel. Permanency can make permanent the effects of enlarge, fear, gust of wind, invisibility, magic mouth, prismatic sphere, stinking cloud, wall of fire, wall of force, and web. 

There are many possibilities which will make the stronghold even more challenging than it otherwise would be, and this can quickly get out of hand. At the same time, this is the place where the NPC lives, so why shouldn't the wizard secure every door in the place with a wizard lock? Some spells will have costly material components or will be too high level to cast flippantly, so these should be treated with special consideration.

For the layout, you might consider using historical castle floorplans. As some of my contemporaries pointed out when I raised this subject, real-life castles are not super gameable. They are impregnable deathtraps which offer very little choice to player characters who might want to infiltrate or assault them, which is by design. They don't make for good dungeons. 

I think that's basically fine, because the types of strongholds in question aren't dungeons and aren't supposed to be. They're what the player characters' own armies of followers and men-at-arms are for - wargaming and sieges. This post isn't about adjudicating mass combat or siege scenarios, so although the topics go hand in hand, we'll leave them for now.

With a good plan the party might be able to stealthily scale the stronghold's walls and neutralize its defenders, or at higher levels they could teleport into the ruler's inner sanctum and confront them directly, but otherwise they'll need an army of their own.

...Unless there was some other way in. I seem to remember a famous D&D module which takes place in a dungeon built under an old NPC stronghold and a passing assumption in the AD&D DMG that player characters (and, presumably, NPCs) will always build dungeons beneath their strongholds. Such a dungeon could not only expand the functional square footage of such a stronghold, but also serve as a secret escape route for the stronghold's ruler in the event of a siege. And where there's a way out...

The dungeon beneath an NPC's stronghold is as important as the stronghold itself. Every NPC stronghold should have one. Like the stronghold above, these should be informed by the character of the NPC who rules it. You might go the B1 route and make this the mad labyrinth of a true dungeon sicko, or perhaps it is a more sensible extension of the stronghold itself - a series of cellars, cisterns, prison chambers, death traps, and treasure vaults. 

Is the dungeon garrisoned with men-at-arms like the stronghold above, or have they captured a menagerie of monsters and locked them down below to deter any would-be besiegers? This might be where the cleric keeps their undead servitors, or where the magic-user has bound their conjured elemental and fiends into service. This might be where most of the thief's traps are laid. 

Through the dungeon, the player characters might gain access to whatever area of the stronghold the ruler calls home. There will be guards to be dealt with inside, but it's still a lot better than storming the stronghold's walls and being peppered with arrows, bludgeoned with falling rocks, and scalded with boiling oil in the mad scramble over the walls. 

The assumption that characters will always build dungeons beneath their strongholds not only provides a more convenient way in for a small band of adventurers, but also a handy justification for defaulting to D&D's default mode of play, where the game is at its strongest. Whether intentional or not, it's a genius bit of design which simplifies a location which poses unique and difficult challenges for the player characters and DM alike.

In a way, strongholds are settlement, dungeon, and monster lair all in one. Preparing one for your sandbox requires you to combine approaches from all three of the former location types along with an understanding of the real-world places in our own history. It is no easy feat, and the resources provided by the game itself are somewhat lacking in this area. If you manage to design a good one, however, you'll be rewarded with a location that can support a variety of modes of play, from social intrigue to mass combat to your usual dungeon fare.

Developing the Sandbox: Monster Lairs

This post is part of my series on developing the sandbox. You can read other posts in the series here. The series will, when necessary, go into detail on the development of my sandbox for Dungeon Module B1: In Search of the Unknown, but will also discuss sandbox development more generally. You can read play reports from my B1 campaign here.

"Wilderness" monster lairs (really "outdoor" monster lairs, since they can appear in inhabited as well as wilderness areas) have much in common with other location types in the sandbox. They're kind of like dungeons, and kind of like strongholds. Monsters can have lairs in dungeons. A stronghold is essentially the lair of its ruler or occupants. The Caves of Chaos is the quintessential monster lair in classic D&D, but it looks very much like a dungeon and plays very similarly to a stronghold, the difference being mainly one of aesthetics and the "personhood" of its inhabitants (i.e., whether or not it is socially acceptable to kill them). The Hall of the Fire Giant King is a monster lair but is also literally a stronghold.

Lairs look different depending on who lives there. A monster lair might just be a room in a dungeon. Outdoors, it could be a cave full of owlbears, which is very obviously a lair, or it could be a leprechaun's burrow, which is visually almost indistinguishable from a hobbit hole. Your character might be a hobbit. To them, that's just a home! Orcs sometimes live in villages, and an enclave of elves is probably like a village too, albeit with a different aesthetic and inhabitants. Giants and vampires and such live in castles. All sorts of monsters can inhabit deserted strongholds.

Despite their similarity to other locations, monster lairs serve their own gameplay purpose and satisfy a unique niche in the sandbox. They vary in complexity. The cave which is home to a small pack of dumb beasts is simpler than the ruin where a dragon slumbers, surrounded by a few dozen sycophantic humanoid worshipers, which in turn is simpler than the underground city inhabited by hundreds of highly intelligent, organized Drow. 

In my own musings on the subject, I argue that monster lairs of lesser or greater complexity serve as "stepping stones" from one level or tier of gameplay to the next. Using my B1 sandbox as an example, the owlbear den offers something for the players to do after they finish exploring Quasqueton, but before they're prepared to infiltrate or lay siege to Fayette's Hold. The ogre den similarly offers a transition from that stronghold - with just a meagre garrison and a relatively less powerful fighter ruling it - to the strongholds of Lambrecht and Blachefleur, the Evil wizard and cleric who hold dominion over the town of Timbershore. If there were also a lair of, say, 300 orcs out there in the wilderness, that would likewise offer some "endgame" content for the players, perhaps after they've liberated the town from its sinister rulers.

Keeping in mind the relative complexity and challenge level of your monster lairs, you can make an educated guess as to which will be easiest to detail and which your players are likely to explore first, which will in turn inform the sequence you should follow when developing these locations. Going by complexity alone, I might first detail the giant eagle nest, Jinglepuff's Burrow, and the owlbear den first, for example.

You can also anticipate your players' likely actions based on the locations' proximity to inhabited lands. Going by this metric, I might first choose to detail any monster lairs found in Timbershore, then take on Zerelda's Camp (yes, a camp of adventurer NPCs is a "monster lair") and the ogre den because they are close to inhabited lands and relatively easy to get to. The giant eagle nest, Jinglepuff's Burrow, and the owlbear den are comparatively remote, so they could wait for later.

In reality, none of these locations should take long to detail, and any of them might become relevant sooner or later depending on the players' interests, so they all end up being developed during the same "phase" of my process. I just kind of jump around from one to the other depending on whichever one interests me next. 

The owlbear den seemed really straightforward, so I knocked that out right away. I had never keyed a leprechaun burrow before, so I did that next because it seemed fun. There was also a monster lair in Timbershore which really caught me by surprise (and which I won't spoil here), and was so delightful that I simply had to do it next. Have fun with it! Keep the momentum going however you see fit.

As usual, I will start with a minimalist sketch of the location. For monster lairs, this includes what type of monsters live there, who their leader is (if they have one), and how the monsters as a group react to adventurers (or the outside world more generally). 

Are the bandits led by a fighter? A wizard? A cleric? Are they actively riding around the countryside, killing, looting, and burning, or are they simply threatening and demanding tribute? They might be Robinhood types, stealing from the rich to give to the needy. Are the orcs causing problems, or just keeping to themselves? Are the elves reclusive, or interested in trading with the human population? Just because the "monsters" are not hostile "enemies" doesn't mean the place where they live isn't worth detailing!

Next, I'll hammer out specifics, like the number of monsters present and what treasures they possess. If you're using something like AD&D, the Monster Manual will simply tell you these things, which is awesome (keep in mind that the actual number of monsters appearing compared to the total possible number will affect the amount of treasure they have). X number of goblins appear in dungeons, Y wandering the wilderness, and Z in their wilderness lair. If they're in their lair, they have so and so leaders and a such and such percent chance to have this or these monsters as guards. It's great stuff.

You might be using some other resource depending on your system of choice, in which case you might have to fill in the specifics with your imagination. The thorough procedural structure of AD&D is one of the many reasons I find myself coming back to it when wanting to run a game.

Honestly, if you're running something like modern D&D, the AD&D numbers work just fine. Even if you're running 5e, try having a bandit camp with 200 bandits in it. That will throw your players for a nasty loop when they hear about the bandits plaguing travelers on the road and assume it's a quest hook for 1st level characters with a carefully balanced combat encounter designed for them to easily defeat, only to find that they need a small army to root the bandits out. The number of monsters suggested by AD&D is less about adhering to some esoteric underlying math and more about creating a lifelike world.

Once you know how many monsters there are and how much treasure they have, you will need to figure out how that's all distributed throughout the lair and convert it into a table-ready key. For small-scale lairs, I think it's quite easy. I use a variation of the same "chunking" method outlined in my post on developing dungeons. Let's revisit this table from the AD&D DMG:

In a dungeon, I treat a roll of 15-17 ("Monster and treasure") as a lair. In a 20-room chunk, there will be three of them. In this case, I really only need one. Since there are normally three, what if I just divide the whole table by three?

Since there are normally 12 "empty" rooms per three "monster and treasure" rooms, my smallest lair needs only four "empty" rooms. There is about a 67% chance of there being another room with just monsters, and about a 33% that there is a "special" room, a trick or trap room, and a treasure room, respectively. That means your smallest monster lair is most likely going to have about seven rooms (four "empty", one with the primary inhabitant and its treasure hoard, probably one with another monster, and probably at least one special, trick/trap, or treasure room).

This works pretty well for a single leprechaun's burrow or an owlbear den with just a mated pair and their cubs. If the lair contains 300 orcs, you'll obviously want to adjust it up so that there's room to breathe. You also don't need to take it too literally - just because there's only two "monster" rooms doesn't mean those are the only two rooms with monsters in them. There is probably an ogre monitoring the room with the hidden pit trap and another standing guard by the treasure den. This is where they live. Spread them out!

You will also want to loosely interpret the results, since this isn't a dungeon. The number of "monster" rooms isn't actually telling you how many monsters are there, since the Monster Manual (or whatever is available in your system) is probably providing that information. Those are just the rooms where the monsters congregate (i.e. where they eat or sleep). 

A "trick/trap" room isn't going to feature the same sorts of tricks and traps you'd find in a Mythic Underworld-style dungeon, but rather whatever sorts of devices the monsters in question might employ in their home, depending on the type of home they keep. These might be proper traps or simple obstacles, fortifications, wards, hazards, etc. Kobolds will set traps in their lair, but owlbears won't. A "trap" in an owlbear lair is going to look like something different. Similarly, the "special" room in the owlbear's lair might be a forgotten druid's shrine in the back of the den, accessible via a narrow tunnel, which offers some boon entirely unrelated to the owlbears themselves.

All this method is doing is providing the number of rooms and the proportion of gameplay features to include. For example, let's say I roll some dice and determine that, in addition to the requisite four empty rooms and the room where Jinglepuff is found with his treasure, his lair also contains an additional "monster only" room. 

Since Jinglepuff is the only leprechaun who lives here, and the Monster Manual doesn't suggest that leprechauns keep other monsters in their lair, I refer to my indexing of AD&D 2e monsters by level. According to that, leprechauns are a 5th level monster, so I go looking for something comparable that might reasonably be found there as well. Blink dogs are also 5th level monsters, and are associated with fey creatures, so I might decide that Jinglepuff keeps a mated pair and their litter of pups as pets (great for capturing and selling into slavery).

If I were to have the same rooms in my ogre den, however, I might say that the "monster only" room is just where the majority of the ogre rabble congregate to eat and sleep, while the "monster and treasure" room is where the chieftain and his favored consorts and bodyguards dwell. This is because the ogre lair contains more than a dozen ogres, while the leprechaun lair has just one leprechaun. In the former example, I'm spreading out a greater number of monsters across multiple rooms. In the latter example, I'm bolstering a single monster's numbers with additional pets and guardians which make sense for that monster to keep.

For a lair of 300 orcs, I could do a full 20-room chunk, with huge garrisons of orcs living in each of the "monster only" rooms, and the chief and sub-chiefs (or whatever) making their own individual "lairs" in the "monster and treasure" rooms. That's still 60 orcs in each room (or, more accurately, 60 orcs spread out across the rooms each group is responsible for protecting), so I might make it a lair with 40 or 60 keyed areas - as I said, these larger lairs can become very complex! 

This also prompts me to consider turning each of the sub-chiefs into their own factions within the larger orc band, since each has its own mini "lair" within the greater lair. This allows for more social gameplay and for turning one faction against the other to start an internecine war between them, not all that dissimilar from the Caves of Chaos. Might I suggest using opposing reaction rolls to determine how the different monster groups feel about one another?

Remember that just as strongholds and settlements assert their dominion via patrols, monsters will control their territory as well. Put some wandering monsters from the lair on your outdoor encounter tables. When monsters are found in a given area of the lair, note if who or what is there differs by time of day. If one cave is where the owlbears sleep, they're probably not there at all times. Perhaps one goes out to hunt for part of the day, while another stays behind to watch the cubs. Orcs hate sunlight, so you probably don't want to raid their lair during the day when everyone is home. If you go at night, some will be out hunting, which will make the raid that much easier.

Many of the same principles you might keep in mind when designing a dungeon apply to designing a monster lair. Jacquays it. Create a wandering monster table. Make sure the "empty" rooms still have interactable elements. If possible, include something to talk to, something to kill, something to be killed by, and a secret to find. 

You'll want the place to feel like what it's supposed to be - a place where monsters live. This is not the Mythic Underworld, impossibly old and inscrutable, with weird rules of its own, where the ancient and alien nature of the place can explain away a lot of the weirdness in layout or features. If your dungeon is filled with undead or fiends or elementals, you probably don't need to worry much about dungeon ecology, but a monster lair is usually home to a type of monster which is much more grounded in the physical world and its requirements - humanoids and beasts that need to eat, drink, sleep, procreate, raise young, go out and hunt, entertain themselves, make themselves comfortable, and the like.

Just as dungeon history informed the specific way in which I stocked my hypothetical dungeons in my previous post, the nature of the monsters that dwell in the lair (and the nature of the lair they dwell in) will inform the way in which I stock their lair. Elves will use magic and warp natural features to suit their needs, dwarves will use shifting stone and have lots of room for crafting, and halflings will keep cozy lairs with full larders. Orcs will decorate the place with the skulls of their enemies, kobolds will employ lots of traps, and cackling will echo through the gnolls' warrens.

Another key element is to ensure the lair suits the monster's strengths. This is probably less so the case in a dungeon, where the monster is more likely there by happenstance, and some other creature originally designed the space for their own ends. The monster chose its outdoor lair for a reason, or modified it to suit its needs. Giant spiders will carpet the floor with webbing to detect prey entering. Fire giants will carve channels for molten lava to form moats. Black dragons will flood some portion of their lair and keep their treasure on the far side of a submerged tunnel. A beholder carves tunnels using its disintegration ray, and it can levitate, so it isn't creating its lair to be easily navigable by pitiful grounded bipeds.

Not all lairs are dungeon-esque. An informal camp home to adventurers, bandits, berserkers, or the like it not going to play like a dungeon crawl at all, nor is a giant eagle nest situated in the branches of a tree atop a tall bluff. These are much simpler, and you can probably imagine easily enough what the place looks like once you have the specifics figured out.

Monster lairs are excellent sandbox fodder, which is great, because you'll probably have a good amount of them, depending on the method you use to stock the sandbox. I determine the number of monster lairs based on the terrain. They are less common in grasslands and desert, but more common in swamps and mountains. If my sandbox is in a more "rugged" "untamed" region, there will be more monster lairs.

They vary in complexity, but are not overly complex until you get to the huge humanoid warrens and villages. At the lower end of complexity, they're dungeonesque, offering turn-based exploration and heated skirmishes in narrow confines. These are not overly difficult to bring to fruition. At the higher end, they're akin to strongholds, forcing the player characters to accumulate power and bring real strength to bear to lay siege to them. These will require significantly more effort to design.

Because there are so many different types of monsters, and each monster will have its own unique version of a lair, they also offer a variety of thematic flavor which will keep your campaign interesting. Bear caves, elf villages, ruined giant strongholds, ankheg burrows, giant beehives, ghoulish graveyards, vampire castles - these are all lairs, and they're all wildly different because of who lives there.

Monster lairs are great because they affect the world around them. Most dungeons are kind of just there. The players will want to explore them because that's what the game is about, and because that's where the treasure is. Monster lairs also have treasure, but the game is also about dealing with monsters, and the lair is where you deal with them. 

That doesn't necessarily mean killing them. You might visit the goblin lair because the goblins have a powerful shaman who can cast a spell you need. You might wish to recruit them to attack the "civilized" frontier fortress where the really good treasure is kept. Maybe the local ruler wants to incorporate the goblins into their territory, the goblins are on the fence, and you're being sent to negotiate terms. Maybe the goblins are ruled over by the neighboring ogres, and they ask you to deal with them.

Be open minded about your monster lairs, what the monsters want, how they affect the world, and how the powers that be feel about them. That will color the way in which you expect the players to interact with these locations. Unlike dungeons, which monsters inhabit almost incidentally, lairs are where monsters choose to live. Why have they chosen to live there? How have they made the place their own? How has their choice to live there affected their neighbors? What, if anything, is to be done about it?