Yes, I am a fanboy.
1. Temple of torment: Hazardous microorganisms, seven riddles told by doors, timetraveling PC's tries to stop themselves from finding the treasure, the treasure is the monster.
2. Pits of monster spawning: Mad science endorsed by the queen, hidden below multiple layers of dungeons below secret recreational castle, the beloved fifteen-dog, mutagenic soup turning spells into monster parts (magic missile-orc, wish-gargoyle...), the beastmaster is shunned in a hundred nations, no exit, only entrances, the treasure is magic components.
3: Hive of the crystal stingers: Giant sevendimensional bees, sub-real-honey, madness inducing passages in honeycomb like structure, lost party of ancient wizards are desperate for aid, exits in magic summoning circles of binding, talking to animals is the key but also a trap, godlike power for the taking.
4: Temple of the free will: Enter freely or not at all, psychotic monks presents impossible challenges that PC´s are free to refuse, six books to be found, six demons to be seduced, ghosts of dead adventurers offer cryptic and misleading warnings, the boss is a dragon-lich, DO NOT ENTER!
5: Cave of the swampwife: Snakes and spiked pits, stickfigure rock carvings of dying adventurers are warnings, strange eggs to be found and hideous mother-creatures to be eaten by, the tides drowns the caves every 24 hours, golden fungus lures adventurers deep into the caves, rotting rust monster zombies are plenty at the bottom, the hideous swampwife kills everyone who does not propose, rubies worth 2d100 GP is her dowry.
6: Golden wing: Crashed partly subterranean spaceship, robots of unknowable designs, alien potion replicators, illusions of treasure and adventure, a lost tribe of elves live in the vast structure ruled by a bald "captain". The treasure is making it spaceworthy again (and boldly go where no Halfling cleric has gone before).
7: Halls of the cat: GIANT dead petrified cat looking like mountain, horrors burrowing and mewing, stenchmonsters and swallowed golems with jingling bells, actually lost familiar of seriously Giant Stoner Space Wizard, yes there are Goblins, and Dwarf necromancer-miners...
8: Dungeon of the Dragon: Ominous entrance, dire warnings, portents in the sky, the most remote mountaintop in the country, bones and signs of combat everywhere, ghost speaking gibberish, actually home of Gnome illusionist, but a real dragon is interested.
9: The pirates cave: Entrance is a barrel, retina scanner only opens for eye-patch, legcutting and handremoving traps, vicious sub-parrots stalk the halls, the Rum is poisoned, imprisoned Viking-ish group of possible turncoats to be found, pirate captain actually Hydra in disguise, serious amounts of booty.
10: Archivarium of origins: Map to this structure found in pits of monster spawning, beautiful surroundings, helpful clerics and paladins of strangely familiar god guards the entrances, top levels are open to the public, sub levels guarded by Werehydrachimeras and signs of "no entry", giant vats of pacified mutagenic goo, traps are elaborate but merciful, bound demonlord slowly writing down everything about everyone's genealogy, boss monster is the god and the treasure is vast but probably unusable knowledge.
11: Subway of the future (megadungeon): Timetraveling future hyper civilization preventing infrastructure failure by building expanded subwaysystem before their rise to prominence, cyberneticaly enhanced Dwarves leads golems and wizards, have accidental bored into Drow and Formian kingdoms and are now locked in never ending (?) war, strange wagons transports PCs in the strange complex, no traps but tricks like talking maps and moving stairs, "tickets" might be needed to pass gates, subterranean horrors slithers in the darkness, gate to the future to be found, terrorists from the future to be allied with, some of the possible bossmonsters are: Meca-blue-dragon, the king of future mutant hoboes, the hivemind clerics of the "cult of progression" and the extremely "modern" glittering vampire. Treasures are plentiful.
12: Tower in the valley: Found by spotting the structure from a distance, surrounded by silent woods, entrance unguarded, signs of recent habitation, lots of mundane equipment and weapons, whole valley actually trap set by tribe of hill giants, when adventurers enter tower they arrive at valley in d4 hours, ready for a feast of low level flesh! They love playing siege with "the walking Tapas"...
Thanx to TDD for the inspiration.