I was thinking about a megadungeon set in and on a giant that fell asleep for countless aeons and became a mountain, with dungeon levels being each of the various chunks of the mountain's surface (canyons and gullies and cliffs forming "rooms") and then the various caves, mines, and excavations into it (and eventually, into the giant itself still sleeping under all that dirt). The end boss is a giant red dragon who has dug into the top of the mountain to build its nest, and is currently laying eggs in the brain of the giant. Because of the red dragon, the giant's mountain has become a volcano and threatens everyone around. Your job is to get the dragon out of there so it stops being a volcano, or at least get rich enough to get away from the eventual eruption (a continent or two should do). Add some wizard towers, goatmen forts, etc. and other tough foes who control the major approaches, a forest full of people who've been hung and come back as undead, ice elves, obsidian men made from shards of the giant's brain, a major trading route that passes beside the mountain, and a small town of locals who profit from that trade, and I think you've got enough for a full megadungeon plus surrounds. Anyhow, I'm tentatively titling it "Feuerberg" ("Fire Mountain").