Konsumterra over at Elfmaids & Octopi has come up with some random tables for Mobile Citadels. I was inspired to come up with some myself, though most are inspired by other sources.
D20 Mobile Citadels
1. Giant steam-powered spider catches slaves with net cannons. Abdomen of spider contains wild west gold rush town.
2, Sea Tortoise with underwater city dome home to lost tribe of Atlanteans with failing super science.
3. Flying colossal manta ray with space city of cosmopolitan traders.
4. Gigantic flying stone head home to dimensionally shifted city inside mouth. Jaded, hedonistic, immortal psychics, sends forth diaper-clad warriors with firearms who raid for food.
5. Animated mountain grinds its way across continent ruled by bickering wizards in their caves and towers. Mountain is dissolved by sea water, so avoids oceans.
6, Mined out asteroid home to space pirates who raid and pillage on flying skiffs and barges before returning to space.
7. Floating rock citadel of doom flies around dropping bat-winged lizard men and dragons.
8. Giant coral atoll ripped from sea flies through the air, lagoon still intact, blue hole inside lair to monstrous lusca (sharktopus) tribal villagers raid surface below for sacrifices.
9. Flying rock island with immense palace and gardens tended by flying, two-tailed squirrels and amazonian bio-mecha warriors.
10. Death from Above, giant adamantine castle hovering on four anti-gravity legs drops humongous rocks on those below. Home to hover bike riding gang of aerial knights and their Sorceress-Queen.
11, Force field domed city on tripod legs stalks land, capturing surface dwellers with mechanical tentacles and blasting with heat rays, home to alien race fond of anal probes.
12. Solid cloud island home to witches coven flying on rocket-powered brooms with their flying monkey minions attack children on surface. Island covered in evil trees, talking mushrooms, and other bizarre living plants.
13. Flying iceberg with bottom dimensionally shifted home to hot spring warmed city of viking warriors with armored polar bears and killer whales warring with 'eskimos' aided by penguin-men and giant walruses.
14. Colossal scorpion home to tent city of desert nomads raiding across the land for slaves.
15. Giant robotic horses pull equally giant gypsy caravan that transforms into traveling circus.
16. Mountain-sized world tree crawls across land. Home to fire giants and ice giants who live in the upper branches in a city where the streets are rainbows. Light elves and dark dwarves used as slaves, while wights and draugr fight trolls and grendels amongst ever-moving roots.
17. Giant moth home to city of miniature people who all identical twins, triplets, quadruplets, and octoplets. The ruling priestess caste uses the moth's poison spray to attack other giant creatures.
18. Nuclear powered land leviathan slowly rolls across land on giant treads. Mutated nhabitants scour land for radioactive materials to feed the radiation furnaces of their home.
19. Time traveling City of the Gods home to Morlocks and Dagon-worshipping Deep Ones warring over Eloi food stock. City appearance means raiding parties from both sides scour country side for food, slaves, and weapons.
20. Cyclopean solar-powered ornithopter flies across land. City of Gold on back home to mutated Olmecs who raid surface settlements for sacrifices on their great pyramids using 'weapons of the sun'.
Ten More Additions
21. Giant Hovering Butterfly Cocoon inhabited by buterfly themed king and his flying minions.
22. Humongous flying beehive full of Zombeez and their queen.
23. Gargantuan floating wasp nest full of giant mutant tarantula hawk wasps.
24. Colossal Land Octopus with giant spherical aquarium for a body crawls across the land. The aquatic inhabitants take great interest in the surrounding scenery.
25. Huge stone sphinx walks across the land. Those that block its path are assaulted with heat rays from the eyes, sonic attack roars, and megaton stomps. Inside are a maze of burial vaults, crypts, catacombs, sarcophagi, speulchres, and ossuaries through which strange humanoids with hawk, ibis, cow, cat, lion, cobra, crocodile, frog, hippo, jackal, vulture, fish, mongoose, and ram heads stalk, battling giant scorpions, carnivorous apes, ravenous crocodiles, fierce dwarves, plagues of scarab beetles, serpentine dragons, rampaging bulls, sexually aggressive baboons, dire golden praying mantises with ruby eyes, phallic consuming elephantfish, sandmen, mummies, Typhonic Beasts, poisonous serpopards, and land-bound phoenix birds.
26. Hill-covering eight-headed and eight-tailed land dragon. Among the labyrinthian internal organs, clans of fierce warriors and proud monks battle black-shrouded assassins and tattooed ruffians. Crazed mountain wizards, sorcerous hags and white-robed priests aided by virginal maidens choose sides in the wars, aided by crow-men, turtle-men, shape-shifting foxes, twin-tailed catgirls, prankster racoon dogs, cannibalistic giant spiders who can appear as beautiful women, and red and blue ogres. Meanwhile a variety of ghosts and goblins as well as living umbrellas, lanterns and musical instruments watch from the sidelines.
27. A massive wooden junk sails across the sky. Amidst the golden pagodas, koi ponds, coral palaces, jade temples, and cedar shrines are massive treasure vaults full of lucky talismans, sacred scriptures, gold, magical cornocopias of food and drink, gems, enchanted tools, and jewelry. These are well guarded by seven powerful beings and their talking animal servants.
28. Monumental human skull ambulates across the land on thousands of tiny legs. Lava streams from the red-glowing eye sockets and it's cavernous mouth is enshrouded in darkness. Within are the factories and furnaces of the enigmatic metalmancer, an antediluvian colossus served by his gold and silver automatons, steel spiders, bronze scorpions, brass crabs, lead leopards, copper centipedes, clockwork homunculi, and steam-powered beetles.
29. Giant Jack O'Lantern propelled by hundreds of leafy vines. From the hell-lit monstrous maw pour forth hordes of boggles, barguests, dullahans, banshees, boggarts, spriggans, korrigans, hobs, bloody bones, shellycoats, dobbies, fetches, kelpies, hell-wains, melch-dicks, knockers, rawheads, ouphs, pad-foots, sprets, spunks, bygorns, waffs, gallytrots, peg-powlers, gallybeggars, madcaps, redcaps, cauld-lads, death-hearses, kows, nacks, brown-men, wirrikows, mannikins, korreds, trows, nisses, nicknevis, and lubberkins in search of 'honored guests' to enjoy the delights of their techno-fey rave.
30. Alabaster colossal statue of a nude woman, with sapphire eyes, ruby lips, and [REDACTED]. A variety of slimes, oozes, molds, jellies, and gelatinous cubes are continually vomited forth from the mouth. Meanwhile, purple, gray, and red worms are frequently excreted. Visitors to the mazy tunnels within will find the door to Wonderland (or perhaps, A Red & Pleasant Land).