I’ve been thinking a lot about dungeons lately, mostly because of the work I’ve been doing for Dungeon A Day. It’s cool, after many, many years of mostly hitting dungeons in passing, to be spending a great deal of concentrated creative energy on dungeon encounters. The dungeon is a unique environment, and decidedly old-school.

You can find dungeon design advice all over the net, and one of the first things almost everyone says is to first decide what your dungeon was originally built for. Few of these site, however, offer more than one or two suggestions, so I started putting together my own list.

Here’s what I’ve come up with:

Bunker: A cataclysm was predicted, and someone built a shelter to survive it (this concept is the entire backstory of FASA’s old Earthdawn game). The dungeon is filled with the wonders (or horrors) of a past age. Or it’s been looted. Or both. This concept works fine regardless of whether the expected cataclysm ever actually occurred.

Cavern: The dungeon is made up of naturally-occurring caves and passages, which have then been populated with monsters or used for any of the other purposes here.

City: A race of underground-dwelling creatures (dwarves being the stereotypical example) built a habitation here. A creepier alternative: An above-ground city was buried in lava or sunk into the earth by an angry god. (Or it burned down, fell over, and then sank into the swamp.)

Farm: Something grows underground, and something else eats it. Might be a kobold fungus farm, or for a really cool example dig up a copy of Michael Shea’s Mines of Behemoth.

Gauntlet: This dungeon was created as a testing grounds, pitting its visitors against ever-fiercer challenges for their training or the amusement of onlookers. Jabba’s Rancor pit is a mini-version of this; the classic labyrinth, of Thesues and minotaur fame, is a larger example.

Hell: Well, why not: the classic Christian hell is, after all, underground, and it follows in the tradition of a body of pre-Christian myth. The dungeon—unless it’s really huge—is just a small part of it.

Hiding Place: Something or someone needed to be kept out of sight. Where better to do that than underground?

Laboratory: A mad wizard (or scientist) needed a place to pursue his or her studies away from prying eyes—or to keep dangerous experiments away from a vulnerable population. Or maybe it’s a proving ground, a place to test weapons or other destructive magics or devices.

Lair: Creatures lived here. The passages and chambers were carved or adapted by orcs by the thousands, or giants by the dozen, or a single beholder or dragon, perhaps with a cadre of servants and guards.

Mine: Long ago the dwarves sought elusive veins of mithril under these mountains. Or the desiccated body of a fallen god. Or the center of the earth, rumored to contain riches beyond measure.

Nursery: Someone wanted to grow monsters, perhaps as shoggoth-like servants, or perhaps to build an army of Uruk-hai. Where better to do it than away from that bothersome sunlight and all those nosy neighbors?

Pocket Dimension: The dungeon isn’t really a dungeon at all, but rather an incursion by some other realm or reality that has taken form underground. An Ars Magica regio fits this bill nicely.

Portal: A gateway to another dimension or location was built in this underground complex. Or the complex was built to give access to a naturally-occurring or long-forgotten gateway.

Prison: The classic dungeon, is, or course, a prison. But what was this one build to contain? A creepier alternative: An asylum.

Repository: Something of great wealth or value needed a home—some place secure. Perhaps a single, valuable object. Perhaps a library or collection. Perhaps something dangerous, from which the above-ground world needed to be protected.

Sewer System: This one’s as old as gaming. Beneath the city streets lies a network of sewers, used as an expedient travelway by thieves and assassins and haunted by ghouls and gators.

Stronghold: Someone needed a fortress, and a castle wasn’t exotic enough. (Frankly, a castle doesn’t make much sense in many high-magic settings, anyway.) If not a classic fortress, then perhaps a Helm’s Deep-style refuge, or a military outpost. Or even a Maginot Line-style border defense (a natural for an Eberron-style setting).

Temple: The dark god demands worship. Underground. An interesting alternative is a monument to a person or event.

Tomb: You can’t go wrong with this one; it practically writes its own script. From Tutankhamun to the Tomb of Horrors, there’s plenty of precedent in real life, fiction, and gaming. A less-explored alternative: the ossuary. Check out catacombs of Paris for all the inspiration you’ll ever need.

Transit Route: A haunted Chunnel. Someone built an underground route from point A to point B. Moria (though principally a city/mine) served this role in Lord of the Rings. An alternative is a sort of fantasy underground railway—a literally underground route designed to let someone move without being detected by those aboveground.

Undercity: This was once the street level, but the city grew up above it and the lower regions fell into disuse (or became a sordid and disreputable underbelly). Perhaps the city above has since been abandoned or destroyed.

These are just a few ideas, but they cover a lot of bases. And they can (and often should) be combined: The mine stumbled into a portal; the sewers are also a transit route; the temple includes a gauntlet for the torture of prisoners and a dungeon for keeping the next batch of sacrifices. Or they change in purpose over time: What was originally a tomb became a temple.

What have I missed? What other major categories might there be—or what additional variants might be spun from the categories here?