Building 7 rooms

BRASS ROSE:  PLANT
SLIME BEAR: MONSTER
FIRE MANTIS: VERMIN
MAGMA DEVIL: HUMANOID
BONE TROLL: BOSS
GILDED EEL: CRITTER

A
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E--C--B--D
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G F
Room A.
SMELL: Faint caramelly smell of exotic woods.
MAGMA DEVIL games room. Mildewed cardboard boxes, rotting tomes with amusing titles like Ye Olde Playeres Handbooke. Spotty MAGMA DEVILS hunched over reasonably flat rock playing Humans and Hamlets with dice made of bone and precious stones. One of the dice is actually lucky.
Room B.
Couple of sorry-looking MAGMA DEVILs roasting FIRE MANTIS over fire. In surprisingly good mood, will share. If you get sick and pass out from the feast they will definitely kill you, but otherwise harmless.
Room C.
SMELL: Vomit.
SIGHT: Everything is coated in fine layer of snail slime.
Dungeon cenote. Sides overgrown with BRASS ROSE, climbdownable. Beautiful turquoise blue water. Bioluminescent bacteria intelligent, psychic, capable of projecting terrifyingly potent hallucinations/activating devotional centre of brain to make you think you see God. Bottom of cenote littered w/ human skeletons from sacrifices. Bacteria feed off flesh. One exit through underwater tunnel, skeleton in tunnel clutches bag of diamond dust and wears water-damaged COWL OF THE ELEMENTS. MAGMA DEVIL cultists soon to return.
Room D.
SOUND: Gloop of bubbling mud.
Map room. Globes, nautical charts, atlases, blueprints, guidebooks. BONE TROLL studying X-marked plan of faraway island, so enthralled that it has difficulty noticing PCs. Exquisite rug on room's floor seems like abstract pattern, careful study reveals it to be map of dungeon itself.
Room E.
SOUND: Howling laughter, swiftly fades to nothing.
Actual dungeon, exists to hold prisoners. Guarded by pair of MAGMA DEVILs, one sleepy, one watchful. They are siblings. Couple of human captives in pitiful condition, starving in cells. One is PHOEBLANTA the TATTOOED ASSASSIN.
Room F.
Enormous mirror is scrying-portal to alternate realms. BONE TROLL getting stern lecture from overboss in Plane of Chaos/other, better dungeon/Hell, will shortly emerge in extremely foul mood. If there is a mirror anywhere else in the dungeon this mirror will let you look out of it.
Room G.
Single incredibly-intelligent MAGMA DEVIL has found only space in dungeon where it is possible to just sit and think. If left to own devices will rule own kingdom on surface world in ~10 years.