In the Abandoned Watchtower

d12
1. Amorphous demi-material entity shunted in from adjacent dimension fills entirety of tower, uses stone structure for protection as per hermit crab, demands aid for return to home telepathically but due to hopeless language barrier just projects incomprehensible nightmares/hallucinations into fragile human minds
2. Giant beehive, floors subdivided into hexagonal cells, queen occupies vault below, worker bees swarm, kill any creatures nearby, masticate and dump near tower to fertilize surrounding garden of immense, preternaturally beautiful blooms
3. Ghosts of long-dead former occupants remain vigilant, send off incorporeal riders w/reports to extinct city-state, unaware of current condition, offer lodging to travelling adventurers, pantry items past sell-by date
4. Magical seal applied ages ago in desperation during disastrous siege proved watertight, tower and dungeon beneath gradually filled w/rainwater, developed self-contained ecosystem featuring squid-like aqueous fungi of dim but measurable intellect, piranha-men locked in Darwinian struggle
5. Retrofitted into inn and hostel for creatures of evil, echoes of unsavory dance music emanate forth into the wee hours, troll bouncers, witch proprietor, bitter humanoids turned away at door plot vengeance
6. Occluded by accumulation of giant spider webs, colony surges forth in scrambling waves for nightly hunt, once-abundant prey in surrounding lands now depleted, increasing number of mysteriously depopulated villages in region
7. Nesting site for flock of undead vultures, hunker down during daylight, search for carrion by night guided by red searchlight beams from empty eye sockets
8. Extremely large giant tore off roofing, uses as personal rubbish bin, filled w/partially chewed knights, large sacks of bones, broken clubs, vast soiled/hopelessly threadbare garments, stolen goods and items too small for giant's use, smashed spitefully
9. Colossal serpent in deep torpor coils within, bloated mass occupies most of the interior, rouses from slumber if exposed to sunlight by opening doors, shutters, first act upon awakening: projectile vomits half-digested tribe of humanoids
10. Gustus Greengills and his band of Jolly Banditos moved in a while back, utilize secret tunnel entrance exclusively, allied necromancer provides permanent obscuring fog, zombie/skeleton platoon to throw off local constabulary by giving appearance of active haunting
11. Evil dwarf engineers conduct preliminary testing of new siege weapons (black powder-charged battering pistons, giant grappling hook launcher/winch apparatus for pulling down walls, etc.), feeble but active resistance provided by debased humanoids sheltering within, exceedingly rare/terrible peals of dwarf laughter resound throughout area
12. Sorcerers gather for annual conclave, await arrival of keynote speaker from alien plane, actually entity planning to consume attendees, process and extrude them as single titanic super-sorcerer capable of world-wide conquest to precede annexation from beyond