Maybe Farum Azula?
Crumbling Farum Azula is a late-game legacy dungeon populated by Beastmen enemies, dragons, and Maliketh, the Black Blade. In the base game, you wake up here after helping Melina light the Flame of Ruin to burn the Erdtree. It’s a floating city, entirely separate from the Lands Between, with a violently rotating tornado near it that will teleport you (possibly through time, it’s unclear) to a big boss fight with the Dragonlord Placidusax.
We learn that Farum Azula was once the ruling place for Placidusax, who served as Elden Lord at one point in time. If this is, indeed, a pre-crumbled Farum Azula, intact and still connected to the Lands Between rather than floating above it, we may learn more of the Dragonlord’s story.
