What about that un-triggered God-trap on the Isle of Terror that Tar-Baphon built?
If anything screams Mega-Dungeon to me, it's that.
And thats why i must recommend something insane: All Megadungeon sites are entry points to the same 'gigadungeon'.
Dungeons are a naturally occurring phenomenon that results when a portal to the Plane of Elemental Dungeon opens deep beneath the earth. As a result, dungeon spills out into the Prime Material plane, causing disturbances in the local reality, such as unlikely hallway configurations, monsters living for years in tiny isolated spaces, a general lack of restrooms, and vast quantities of inexplicably minted metal coins.
And thats why i must recommend something insane: All Megadungeon sites are entry points to the same 'gigadungeon'.Dungeons are a naturally occurring phenomenon that results when a portal to the Plane of Elemental Dungeon opens deep beneath the earth. As a result, dungeon spills out into the Prime Material plane, causing disturbances in the local reality, such as unlikely hallway configurations, monsters living for years in tiny isolated spaces, a general lack of restrooms, and vast quantities of inexplicably minted metal coins.
LOL
And: +1 mega-dungeon AP