The second key to good dungeon design is variety. Dungeons are big and players don’t want to fight the same encounter over and over again while clearing them. Even if you have a one-page dungeon that’s just the lair of some orcs, you should still include enough variety to keep things interesting. Use an Eye of Gruumsh and an Orc Warchief as boss encounters in certain rooms, give some orcs longbows instead of greataxes and have them engage at range while their standard orc buddies hold the frontline, give some orcs dire wolf mounts to make them into powerful cavalry, and now you have five different encounters (including the standard “just a bunch of orcs”) without even dipping into room design, traps, making unique monsters, or having multiple factions in the same dungeon.
Room design is an important part of encounter variety, but make sure your monsters are able to use the room’s layout to their advantage. For example, if you have a sneaky orc ranger in one room, you might make it a large natural cavern, but give it a lot of stalagmites for him to sneak off behind to lose the party if they find him. An orc sorcerer with lots of fire magic might fire on players from a ledge above a cramped corridor where they can’t spread out to avoid his AoEs, then retreat into the side-path leading to that ledge if the players turn out to have some serious ranged firepower of their own. Monsters live in a dungeon, so even if they’ve only been here a week or two they probably know the place well enough to have figured out what areas are best suited to their abilities, and will be assigned there (or just gravitate there naturally if they’re too disorganized to have any assigned patrols or guard stations).
You can squeeze more unique encounters out of the same set of monsters by taking advantage of room design. Using just regular orcs and orcs using longbows, you can have a brawl in a mess hall where the ranged orcs use their melee buddies to keep their distance, a room split in half by a chasm where orc archers on one side will attack the players with impunity if they come into the opposite end, but will be forced into melee if players come through the door on the archers’ side of the chasm, and a bridge surrounded by arrow slits that archers use to soften up the party while a mob of orcs rush across to meet them.
Traps are another way to add variety to a dungeon. You can just let a trap stand on its own, but they’re often more interesting if they’re part of a larger encounter. For example, a pressure plate triggers a fusillade of darts, softening up the party, and then immediately afterwards ambushing goblins leap out to try and finish them off before they can heal. If a trap is going to stand alone, make it a set piece, like a room whose walls close in to crush the occupants or which floods to drown the occupants. Bear in mind believability when designing these traps. Whatever monsters live in this dungeon have to actually build these things. If they can’t make a room watertight, they can’t make a drowning room trap. They’ll need some serious mechanical power to make a crushing walls trap. Also bear in mind that some “traps” may not be intentional at all. A falling bricks trap might just be because the dungeon is old and starting to fall apart. You might have them strike squares at random during a large melee in a cramped area. You can be pretty sure they’ll hit something (especially if one or two of them go off every round), but they might hit the monsters just as much as the party.
Varying the rewards can also keep a dungeon interesting even if the encounters (including their room design and traps) are starting to feel same-y. Players might have fought a half-dozen-ish orcs led by an Eye of Gruumsh twice already, but if the first time they got boots of speed and the second time they got a mace of terror, then by now they’ll have picked up that the Eyes of Gruumsh are the keepers of the dungeon’s magic items, and wondering what magic item this one will be guarding can keep them invested in an encounter that might otherwise be repetitive. This is doubly true because the Eye of Gruumsh will probably use the magic item he’s guarding, which means fighting him might have a touch of flavor to it that sets the fight apart from the other Eyes.
We covered this in the Art of Encounters, but it is important to repeat here: Players decide what kind of encounter any given room will be. If you sense they’re getting sick of fighting through things, you can suggest that they might take a stealthy or diplomatic approach instead. Preferably, a dungeon should have enough variety that even if you just slaughter every creature inside of it, it still won’t get old, but if that fails, encouraging players to switch up their own tactics can help keep content interesting for longer. You can also design some encounters such that they lend themselves more clearly to one approach or another. More specifically, designing some encounters to be more open to negotiation than others can help draw more variety out of a dungeon. The party might stumble across prisoners who, once freed, might be convinced to help you fight against their captors instead of immediately fleeing into the wilderness, or they might find evidence of a rift between the dungeon lord and one of his lieutenants that they might be able to parlay into a civil war.
Most of these tricks will help squeeze just a few extra rooms’ worth of variety out of a dungeon. If you want to keep a very large dungeon from growing stale, you need to have noticeably different areas to the dungeon, with different monsters who fight in a different style with different terrain. For example, hobgoblins tend to directly engage opponents with well-balanced teams that are prepared for many different threats, and will usually take up positions that favor what their group is good at (which may vary from one encounter to the next, as different hobgoblin war parties have different units). They’ll fortify whatever part of the dungeon they’re occupying to better suit their defenses, but they won’t make very heavy use of traps or ambushes, instead using things like chokepoints and reach weapons to force one enemy at a time to fight two ranks of hobgoblins, or using arrow slits in fortified towers to fire on enemies who will have difficulty shooting back. Regular goblins, on the other hand, will have more ramshackle living quarters, and rely more on traps and ambushes.
Orcs will be as straightforward as the hobgoblins, but less disciplined, usually charging straight towards the nearest enemy. They’re plenty capable of some tactical planning in advance, but once the fight starts they’re much harder to control, and their plans will take this into account. Orcs fight for glory, and you can’t expect any hot-blooded orc warrior to stick to a plan that involves hanging back while there’s glory to be had in battle. Ogres are very big, very strong, and not so bright, so they’ll tend to be very bold against creatures smaller than them but more cautious against creatures their size or especially ones larger. Trolls are cunning ambush predators who lurk in narrow crevices and wait for an unsuspecting creature to wander by, then attack the luckless victim in melee, and in tight quarters where escape is difficult.
Examples keep going for as long as the Monster Manual does. Use the culture and abilities of the monsters you’re using in the dungeon to inform how they fight and how their section of the dungeon is built (especially if they built the dungeon from scratch, which means each and every room was placed because they wanted it there). Not only does this improve believability, it more importantly means that going from a section of the dungeon controlled by orcs to a section controlled by goblins will be a very distinct shift in how the opposition fights.
As discussed in the Believability section, different types of monsters can also make different factions who may be anywhere from closely allied to one another to openly at war, and this can open up lots of possibilities for player interaction. Two monster factions which are very closely allied are essentially the same faction, and may even be intermixed in the dungeon. If orcs and ogres get along swimmingly, they’ll probably share barracks, mess halls, and so on with one another.
Two monster factions who formed a coalition for a specific purpose, however, will keep to themselves, and may even turn on weakened members of the coalition if they don’t think they’re strong enough to be a meaningful contributor anymore. Some member factions of the coalition might be more loyal to it than others, and some coalition factions might be convinced to back out of or even betray the coalition. All of this is significantly exacerbated if the coalition is between normally enemied factions brought together by a common enemy or a strong-willed dungeon lord. In the latter case especially, the death of the dungeon lord will probably see the factions of his dungeon coalition immediately going to war with one another.
Just because monsters share a dungeon doesn’t mean they aren’t fighting one another. Dungeons may be in a cold war in which any sign of weakness (say, because players depleted forces) will result in an attack by neighboring factions, who will occupy the territory. Capturing new territory doesn’t give a monster faction new troops out of nowhere, though. They’ll have to stock the new territory by either draining some of their random encounters to make some new static encounters for the captured territory, or else by moving some of their static encounters out of their section of the dungeon and into the captured territory. Either way, monsters who aren’t reckless should weigh the benefits of newly captured territory against the risks of spreading themselves more thin. To adventurers, a dungeon is a pinata full of treasure and blood, but to monsters, it’s a Risk board, and only foolish dungeon lords will make the mistake of going for Asia.
Speaking of random encounters, different areas of the dungeon should have their own random encounter tables, which is another way that one faction controlling multiple areas gets stretched thin – they have to split their random encounters between two tables. If monsters are in a fairly friendly coalition, random encounters from other factions might show up, as a couple of drow drop by to chat with their orc buddies while off-duty or what have you. In dungeons where monsters are actively at war with one another, random encounters might include an incursion of forces from a hostile faction, who might be persuaded to team up with the players for so long as they have a common enemy.
With the possible exception of enemy variety, faction variety is by far the deepest well to increase the variety of your dungeons and keep larger dungeons interesting for their duration.
The third key is non-linearity. In recent years, the dungeon crawl has often been the victim of linear design. The subterranean nature of a dungeon makes it pretty easy to keep players on track, and particularly in the 3e and 4e days it was often considered close enough to a real dungeon crawl to just have some twists and bends in a linear route without actually branching the corridors at all (you get this sometimes in the Adventurer’s League, too, which I hope is mainly because they need to make sure the adventure takes a specific amount of hours to complete and having a very open dungeon crawl would interfere with that something fierce).
This harms believability, because a dungeon is almost always a location that would not have such a linear construction. Whether it was intentionally built as a subterranean fortress or it was repurposed as such from a mine or natural cavern, there’s almost never a good reason for a dungeon to have few or no branching paths. It also removes one of the best sources of fun from a dungeon crawl: Exploration. Deciding where to go next and slowly filling in the blanks on a map. It even harms challenge, because exploring a challenge and deducing where targets are based on contextual clues from a well-designed dungeon is a skill. Even if a party lacks the resources to clear an entire dungeon, they might be able to find the parts they’re looking for with some deduction and/or interrogation. Clever scouting hardly makes a difference if you have to go through nearly every room in the dungeon to reach the goal anyway.
Loops and Branches
The most basic elements of dungeon layout are loops and branches. While a branch leads to two separate areas that don’t lead to one another except by backing up to the branch, a loop is a series of areas that are all connected to one another. A branch provides a simple choice, although if one branch is easily cleared then it’s hardly a branch at all. The party will go down one branch, reach the end, then turn back and go down the other. However, branches can be used to interesting effect if they contain secondary goals (and sometimes it just makes more sense to have a branch than a loop – don’t sacrifice believability on the altar of non-linearity, especially since believable dungeons will be plenty non-linear anyway). For example, the monsters’ treasury might be located behind a series of traps and guardhouses that branch off of a loop in the dungeon, or perhaps there is a lair of a wyvern that branches off a loop in a goblins’ lair.
Loops are the cornerstone of non-linear dungeon design, however, because they provide the choice of going around encounters. This is particularly true if the dungeon has been alerted to intruders. An encounter might do its damndest not to be gotten around, but if there’s a loop, the party can get around it if they’re quick or sneaky enough. Loops let you decide not just what order a party wants to deal with encounters in, but gives them more options for dealing with those encounters and lets them decide if they want to deal with certain encounters at all. Players skipping an encounter might seem like the encounter is wasted effort, but the ability to skip encounters lets players know they have actual freedom within the world, and that is worth the effort of making a few encounters that get skipped.
Hidden entrances, both into the dungeon itself and onto specific dungeon levels, are another way to make loops not just for a few areas but for entire levels of the dungeon. A second set of stairs (or a ladder or chute or teleporter pad or whatever) between levels 1 and 2 turn the entire dungeon level into a loop. Likewise, if there’s a hidden entrance straight into level 3 of the dungeon, then levels 1-3 become one giant loop. Readers might reasonably wonder if potentially cutting out two entire levels of a dungeon isn’t perhaps pushing the limit of sacrificing work for player freedom, but remember, dungeon inhabitants shouldn’t be waiting around to be mulched into XP by the player characters. If the players find a hidden entrance to level 3 of the dungeon and they decide to use it, that means there are two completely untouched levels of the dungeon lying around to make a reserve force out of, and if that reserve force follows the PCs down, they will be between the PCs and the exit. If the party finds a secret entrance between level 3 and level 4 they can sneak around that reserve force, get to the hidden exit on level 3, and slip out without fighting that reserve force, but the key word there is “if.” If the players don’t find that hidden connection between level 3 and 4, then in order to get back up to level 3 they will have to use the main stairwell that every spare monster from levels 1 and 2 (and any they missed on level 3) is now camping on. This is the kind of considerations that make clearing a dungeon feel more like an assault on an enemy fortress and less like a Diablo clone with hideously sub-par action resolution speed.
Sub-levels are when one floor of the dungeon has two or more connectors that each lead to a lower level, and these lower levels do not connect to one another. For example, on level 4 there might be two different stairways down, one leading to level 5A and the other leading to level 5B, but there are no corridors connecting levels 5A and 5B together. One of these might be a dead-end, so for example the stair down to level 6 might be only on 5A, or they might both have connectors leading down to level 6, in which case levels 4-6 together form yet another loop. Non-looping sub-levels can be a good way to cordon off an optional sub-section of the dungeon, especially one that contains some important side goal. Maybe the goal of the dungeon is to kill the monsters’ leadership in the fortress on the final level, but there’s a sub-level branch containing their treasury, including several magic items that none of the monsters can use themselves, but which might be helpful to the party, who have a wider variety of character builds and explore a wider variety of fantastic environments (a driftglobe might not be seen as very helpful to monsters with darkvision and a ring of water walking isn’t very helpful to a monster who lives in the desert, but a multi-racial party probably doesn’t all have darkvision and wandering adventurers are probably going to end up at a large body of water they’d like to walk over sooner or later).
Sufficiently large sub-levels (looping or otherwise) can be dungeons unto themselves. In fact, one way to make a large dungeon in a hurry is to take multiple small ones and Frankenstein them together into a bigger one. You have to be careful about making the seams too obvious, but adding a few connections between a series of natural caverns with goblins, a catacomb overrun by undead, and adding a surface lair that’s a small temple of Tiamat controlled by kobolds and dragonborn isn’t unreasonable. The catacombs were formerly a burial ground for the temple, which was once dedicated to some other god before being seized by the Cult of the Dragon, and some goblins from a nearby natural cavern broke in mostly by accident while tunneling out some new accommodations. Connect the entrance to the catacomb to a room in the temple, then connect a room somewhere in the cavern to another somewhere in the catacomb. The temple and the cavern both have separate entrances. Even if the dungeons were fairly linear before (for example, if you took a few dungeons from the Adventurer’s League adventures for Tyranny of Dragons) adding these connections between them will make them passably interesting.
This is a relatively basic example, and nested dungeons can get much more complex. For example, imagine two (or more!) dungeons that both descend somewhat parallel to one another into the earth. Level 4 of dungeon A connects to level 3 of dungeon B, and further down level 6 of dungeon A connects to level 4 of dungeon B. These kinds of connections are especially useful for megadungeons and won’t come up so much if you’re hoping to use a dungeon as just one adventure.