Nemtox was a planet in the unknown regions. It was more than 3 times the size of a regular terrestrial planet and had 3 times as much gravity. Nemtox was an incredibly toxic, dark and lifeless planet with very strong affinity with the dark side of the force . It was also an adopted homeworld of the Makuta .
The planet was so strong with the dark side that no Jedi could even enter the system without being put in incredible discomfort, and moving closer to the planet would induce nausea and hallucinations. To land on the planet as a Jedi was fatal, regardless of species. Due to this, Nemtox was the ultimate safe haven for Sith, as the Jedi could not pursue them here.
Even the Sith themselves felt discomfort on Nemtox. Darth Vader and Darth Krayt are said to have found Nemtox unpleasant. Darth Sion and Darth Nihilus , as well as the Makuta Teridax and Miserix are some of very few beings who are thought to have enjoyed visiting Nemtox.
Nemtox orbited a black dwarf and a black hole, the remnants of the two stars it had supposedly formed around. Eventually, Nemtox and the black dwarf were consumed by the hole.