If Castle Greyhawk is THE megadungeon of Greyhawk, and Undermountain is THE megadungeon of the Forgotten Realms . . . what is Eberron’s? In terms of a classic dungeon—bounded space, underground, manmade—I'd say the Realm Below of the Mror Holds, an ancient kingdom filled with wondrous treasures that was claimed long ago by Dyrrn the Corruptor.
— Keith Baker (@HellcowKeith) May 27, 2022