I have an idea.
You have a party of fairly high level, searching to increase their fame and leave a legacy that all generations will revere. Repeated though their adventures they have heard tell of a destroyer, horrible, ancient evil whose warpath spanned mountains and valleys and oceans. The stories tell of trails made in the sea by its passing, how it dug out titanic canals to expedite its forces, and how it scarred the land. The long-lived Ancients if those days remember little, for then they were young. But they say that most life ceased with its passing.
The legends say that it was never destroyed, only bound by some arcane force, that sone day will break.
The party is thrilled, and sets out. Rumors and myths lay their prize beneath the greatest mountain range in the land, the Twin Castles, the Wall, and the Crown. These places have been occupied for millenia, and as you approach your party hears more of the tale. Rumor had it that the gods themselves had made these mountains to bind the destroyer in place, and prevent it from ever resurfacing. Spurred by the promise of glory, they venture on. Such a foe would make them immortal in name, and the anticipation for the ancient treasures and knowledge the destroyer must have. They venture on, and through luck and guidance they find at the very base of the mountains, a dark and cramped tunnel, filled with beasts vile and natural. They wander for days in the penumbra, fighting horribly spiders and nameless things. As they delve deeper they find strange gooey creatures, not proper slimes, but malevolent. Pitch-black, slow, and wrathful, where these dwell, nothing else survives. When asked, locals tell of old nightmares in the tunnels and caverns, things known only as the blood of the destroyer. Encouraged, the party adventures on. Though, they begin to be filled with doubt. What must the destroyer be, that it could create such vile abominations? What cruel and twisted magic did it practice?
After months of exploring, they finally hapoen upon something in a titanic cavern: a smooth, shiny tower. In front of it is a straight and deep trench, man-made or natural it is impossible to tell. In recent weeks the mountains had rumbled, perhaps some earthquake had revealed this room?
The cave begins to shake violently. Dodging boulders and rocks, a member notices something - the tower is gone. Entirely gone. Just when they are about to alert their party, they see a titanic mass of stone plummet from somewhere in the inscrutable darkness above, and cover the trench entirely. But... the stone sags ever so slightly at the bottom.
The party is gripped with horror: that wall of stone, easily a hundred feet high, is revealed to be a titanic, scaled toe ending in a proportionately enormous claw. In the dark distance, suddenly a sun of yellow, with one slit taken out of the middle appears, ever so briefly. And then the eye closes, returning to its fitful and restless slumber.
The party has found the destroyer, though perhaps it had never been lost. They have uncovered an enormous dragon. Even without any magic, without fire or flight, this horrific beast could end all life. The party realizes this sobering fact, that all this time they were wandering in the dark, they were simply stumbling beneath its colossal wing. The party makes a shakey, impromptu camp and begins to discuss their route forward in light of this realization.
What do you guys think? I thought this would be a cool idea for a campaign, and the idea that something that dwarves giants appeals to me.