Building 10 rooms

TRUE MOSS:      PLANT
PIT SALAMANDER: MONSTER
HORNED SNAIL: VERMIN
HOOK GHOUL: HUMANOID
HOLLOW MUMMY: BOSS
STAR BOA: CRITTER

G H E
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F--C--A--B
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J D--I
Room A.
Looks like three-doored room. Tarnished mirror in corner will, if cleaned, show secret fourth exit in reflection. If taken to any other room it will also show a secret extra exit in that room. Secret extra exit always goes to same place, no matter where you are in the world. Overuse has chance of awakening evil reflection monsters.
Room B.
SOUND: Burble of distant river.
High ledge w/ two entrances that looks out over vast lake of lava. One HOOK GHOUL peacefully fishing w/ brass rod, wire, hook. If left alone long enough he will catch something. 50% chance of hungry lava fish, 50% chance of lava treasure.
Room C.
SIGHT: Room is part of ancient castle, walls are slabs of stone.
Dungeon oasis. Lake of pure water, grove of TRUE MOSS, STAR BOAs and HOOK GHOULs drinking together in peace. If you start a fight here everyone in the dungeon will find out about it and regard you with unremitting hostility forever.
Room D.
GARELOPA the WHISTLING SOLDIER, playing the flute. Has no idea they're in a dungeon. Can see everything around them perfectly clearly, just refuses to believe it's a dungeon. Will confabulate other things it could be. Flute not magical unless you desperately need it to be.
Room E.
SMELL: Strangely warm, like being in a kiln.
Map room. Globes, nautical charts, atlases, blueprints, guidebooks. HOLLOW MUMMY 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 F.
Hideout for rebellious HOOK GHOULs, unwilling to recognize authority of HOLLOW MUMMY, want to establish tiny republic in forgotten dungeon crevice.
Room G.
SIGHT: Room is part of ancient castle, walls are slabs of stone.
Bedchamber of three, four HOOK GHOULs. Sodden and filthy. Careful inspection of damp rags that serve as bedding will reveal a(n) POET'S LAMP in surprisingly good condition, but forces save against filth fever.
Room H.
SIGHT: Dust on every flat surface.
SMELL: Humans being cooked. Indistinguishable from roast pork except to trained noses.
Looks like empty room. Actually maw of cave leviathan, those weird stalagmites its teeth. Glimmer of treasure deep in gullet is pyrite lure. STAR BOAs pick dead flesh from between teeth.
Room I.
SIGHT: Flowers bloom everywhere, even where they shouldn't. Especially where they shouldn't.
SMELL: Stagnant air and decay.
Lightless oubliette. QUEEKISK the INCOMPETENT SENATOR has been trapped in here for at least twenty years, some HOOK GHOULs coming by to feed and water them occasionally.
Room J.
SOUND: Hiss of steam escaping through cracks in floor.
SIGHT: Room is part of ancient castle, walls are slabs of stone.
HOLLOW MUMMY laboratory. Weird hybrid things bubble away in glass tanks. At least one attempted crossbreed between HOOK GHOUL and STAR BOA. HOLLOW MUMMY not there. VIRION the DEAF WATCHMAN pretends to be experimental captive, is actually willing lab assistant.