From Ardrana

Zarach-Oras is a city of the drow, located somewhere in the UnderWorld. Its exact location is uncertain, but it is known to be somewhere beneath the northern part of Lanad i'Sarois, accessible via a long, winding passage through the Luyan Mountains. It is the largest known city of the Dark Elves, and indeed the largest in all the UnderWorld. It is ruled by a group of drow clans, the number and makeup of which varies constantly, with ever-shifting alliances among them. The last contact with the city was decades ago, thus throwing into doubt any information of its current status.

Note: Zarach-Oras is based on material from the module Vault of the Drow for the Advanced Dungeons & Dragons game by TSR, and was incorporated into Ardrana. Their inclusion here is for the purposes of providing context for the campaign only.