Mustafar, the 'hot spot' for tourists who like it 'hot'
Mustafar is a planet located in the Force Galaxy. It is a lava-based world, with an unstable atmosphere. It is basically one big volcanic eruption.
The Endar Spire's final resting place was located on this planet, making HK-1 the planet's first sentient inhabitant until, after centuries of failed attempts, the Techno Union was at last able to establish a mining colony on the volcanic planet.
General Grievous seems to think that Mustafar is completely safe, and he sent the leaders of the CIS there for safekeeping before he was eventually blasted to death.
Mustafar was the site of the lightsaber duel between Darth Vader and Obi-Wan Kenobi that left Vader hideously scarred. Because of this, the planet has a noticeable Dark Side aura. This energy was later harnessed by Tavion and her minions during her quest to reawaken Marka Ragnos.