Dungeons can be difficult to rationalize. I’ve struggled with the dungeon conceptually (also philosophically) throughout my game mastering career. It’s important when you design a dungeon, to have a picture in your mind of what the dungeon was made for, since comparatively few dungeons resemble modern prisons.
I’ve read a fair amount of literature on the subject of a dungeon’s purpose, and it’s important to start with an idea, to have some trap or some encounter, or some creature in mind before you begin, because dungeons are rarely created without purpose. Take the mythical Greek Tartarus for example, the ultimate prison.
Tartarus is both the name of a place and a name for its warden, similar in many ways to Hades – Hades being of course the Land of the Dead, intended to contain (or imprison) the spirits of those who have passed beyond the mortal world. Both have a purpose — one to contain the threats to the world, one to contain dead spirits.
By far the most common “dungeon” is actually a lair, the dwelling place of a creature or group of creatures. Lairs are rarely trapped except by the most paranoid or eccentric of monsters (more often than not humanoids) because the dungeon is their home. Traps are antithetical to a living space. Particularly deathtraps.
The scope of a lair is proportional to the scope of the beast — a troll haunt is similar in scope to the trolls it houses, while a wight barrow is similar in scope to its wights. The most famous of lairs — the dragon lair — is a staple of fantasy fiction and reflects the age and attitude of the dragon who makes it their home.
Usually the things that make a lair ideal for one monster are ideal for another — if you want to throw the party a curve ball, you can throw a lair at them that has housed multiple monsters. Depending on the term of residence, one monster may carve out new sections of cave, trigger collapses, or “burrow deeper.”
Similar in concept to lairs, you have “sanctuaries,” where criminals, fugitives, and exiles may settle and forge a new life. These are homes too, but are far more likely to have defenses like walls and traps, armed guards, and mercenaries or even personal armies. Mos Eisley from Star Wars or Tortuga from Pirates of the Caribbean.
Sanctuaries are one of the more versatile locations for “dungeon” excursions because they represent a melting pot of competing villains and villainous factions. A sanctuary is a place for a monster to “blend in” or disappear from the prying eyes of the world. They’re also a great place to hire unique individuals with unorthodox abilities.
Then you have “forts,” which can be out-of-the-way places that are the most likely to be guarded, the most likely to be trapped, and perhaps the most like to contain some great treasure like an artifact. Fortresses are more “occupied” than settled but if they aren’t too remote, they might develop satellite towns that offer trade.
Forts are always built with some kind of defensive goal in mind, even if it’s an outlandish one. They often sit on borders, sometimes in hotly-contested areas between countries, usually on hills or cliffs, sometimes with moats or spike-filled trenches, and so on. Usually a forts’ weakness is in how it sustains itself.
Due to the remoteness of a fort and the hostility of its environment, the best method of attack is usually its supply trains or its “thermal exhaust ports.” Attacking a fort often means infiltrating it, but can sometimes mean besieging it — because forts are usually built to defend something. Sometimes a valuable political prisoner.
Keep these in mind when you build your next dungeon adventure – lair, sanctuary, or fort. Two out of three are homes for their denizens.