Zilkhûn is an Underdark city of Batwor. It was built by the Khazarkar Empire a half a mile under the empire's capital city of Nibar-Pharân. Built at great expense, and use of magic, it is a rival commercial port to Bandunazân and Balmoloch. A harbor was dug before the city and then a channel made all the way east to where they then broke a coffer dam, letting in the Erethor Sea. This created an underground port linked to the surface.
Zilkhûn and its sea channel are at the base of the Khirrêth Plateau.