Phaervorul
From Syra D&D Wiki
Phaervorul is an underground city of drow. It was one of many enclaves magically shifted out of Doth'Candorun in 2930 as part of Kiaransalee's attempt at opening their prison.
In 2959, a drow named Zirithian who had turned to Orcus's service assaulted his former home with an army of undead.