The Ebonmurk is an subterranean sea of the Onvorn Region. This dark sea is fed by numerous waterfalls, whirlpools, and waterways from the surface. Some of the whirlpools of Ebonmurk have a reverse flow; anyone entering is taken upwards to the inland Galathien sea. The Galathien has whirlpools that safely transport a vessel down to the Ebonmurk. These magical whirlpools are called the Vortices of Khushnír. They were created during the Horgon Era by a fomorian conjurer named Khushnír. In western Onvorn, the sea is fed by the Nedullu. This wide river starts far north at the southern tip of the Heliotrope Sea

Above and below Ebonmurk are massive stalagmites and stalactites. Many of these formations holds fortified settlements of Underdark peoples. Spread across the sea are numerous islands. It is common to sea boats on this waterway. Some of these vessels are tradesmen from the surface.

There are trade winds on the Ebonmurk. The winds comes from numerous holes and chasms scattered about the surface of the Lands of Purity. Some of these have considerable light. These lighted areas are thick with fungi, plant-life, and the occasional raiders. These raiders use the light to ambush creatures more accustomed to the darkness.