Undrentide

Undrentide was one of the Netherese flying cities that crashed to the earth when Karsus cast the spell that momentarily made him the god of magic. It was buried under the sands of Anauroch and forgotten, until the medusa sorceress Heurodis discovered a powerful artifact that allowed her to reawaken the mythallar that powered the city, gaining its powers to herself but also becoming a lich in the process. The city was setting to the skies again at her command when Drogan's student (the game's protagonist), who had followed her after she killed their master, confronted Heurodis and destroyed her along with the mythallar, fleeing to the Plane of Shadow as the city fell back to the earth a second time.