Im just a bit confused here, is the Sudanesselar in the underdark? Im not very good with the names i sort of went throught that area quickly and wasnt paying much attention, thanks to anyone that can clarify this for me!

Ust Natha is the Drow city in the Underdark;
Suldanesselar is the legendary city of the Elves, located somewhere in the Forest of Tethyr.