The Nightmare Lands constituted a forested section found on the planet of Voss.
Reportedly, the forest's vegetation grew in a thick, tangled manner, and a corrupting force held dominion over the area. This region served as home to wildlife that had become corrupted, Gormak inhabitants who had fallen under the sway of darkness, and insane Voss Mystics—members of the indigenous Voss species. Furthermore, the sinister being Sel-Makor made its dwelling in the Nightmare Lands, specifically within an underground temple called the Dark Heart. It was believed that if the conflict between the Gormak and the Voss persisted, the Nightmare Lands had the potential to spread and eventually engulf the entirety of Voss. In the Northwest portion of the region, a lake held a small island, upon which a meditation shrine and a tablet were situated. Voss Mystics frequently engaged in meditation at this location, seeking to enhance their concentration for entering the Spirit World.
The initial reference to the Nightmare Lands occurred on the Star Wars: The Old Republic media site, accompanied by conceptual artwork depicting the planet Voss.