A wise DM once said, “you’re only as original as the obscurity of the things you steal from.”
So here’s a few ideas I stole from my brother, books, TV, other DMs, and my own campaign notes! These descriptors can be purely atmospheric, or you can use the unique circumstances to complicate things for your players!
I’ve marked the ones I’ve actually played with a ♥, in case you want to hear some specifics of how it went. I’ll be updating this list, so keep your eyes open.
♥ A translucent and fragile-looking spire made of ice, amber, glass, or crystal
The hollowed insides of an old, giant tree (dead or alive)
Above the beanstalk, up in the clouds
♥ A forgotten underground tunnel system connecting two cities
A ruined castle half-buried in snow/sand/earth/water
A Labyrinth, complete with a wandering monster, and a curse which breaks navigational magic
The forgotten corridor between dimensions where outsiders, stragglers, and ideas live
The bones of an ancient, colossal creature
♥ A magic library, with living books and other hazards
♥ An abandoned Frankenstein lab, or construct factory
A high-security bank, prison, etc.
♥ This dungeon seems to appear and disappear at different intervals and locations, meaning coming in (or leaving) is sometimes impossible
♥ Gravity works strangely here. You may find yourself upside-down to the rest of the world, standing on floating platforms that crumble and break in odd directions
♥ This is a pocket dimension with its own set of rules--perhaps literally using the rules of a different board game, arcade game, or rpg
♥ There is a spirit living here who represents the dungeon itself. It is ancient, enormous, eccentric, and with uncertain morality.
The place was built too small or too large for the party (Kobold made, Giant made, etc.)
♥ Magic is distorted here, and spells sometimes cause wild magic surges, or fail entirely
♥ This place has funhouse elements--slides, platforms, and silly, gamey rituals that must be overcome
These are hallowed/desecrated grounds, and as such the land has some effect on holy/unholy magic
♥ This is a malleable mirror/dream world, built by someone’s psyche
Party members swap bodies when they enter. Enjoy your new character sheet!
Local beasties have moved in and built nests
♥ A gang or cult has made this their base
The original host is long dead, but half-broken sentries still patrol...
This place was built and guarded specifically to keep THAT THING contained...i.e. monster types with specific abilities and resistances
♥ There are prisoners who must be evacuated, and monsters which are best left alone...but which are which?
Mostly/entirely abandoned, but prickling with traps and hazards
Note: There’s no reason you can’t mash a bunch from each list together. Have your ruined castle be on the moon. Have your magical library be a shifting labyrinth. Have your mine be harvesting mana from the bones of a long-dead magical creature. It doesn’t even need to make sense--maybe these catacombs were built like a funhouse by a lich with a strange sense of humour. Get weird with it!
My brother’s wonderful holiday one-shot got me inspired to add a little confusion and whimsy into my world, and so I pass my inspiration on to you. Have fun!