The Klegger Corp Mining Facility was a mining facility on Mustafar built on the side of a mountain, overlooking a lava river. It was owned by Klegger Corp, which in turn served the interests of the Techno Union.
At sometime during the the Clone Wars, the Confederacy of Independent Systems constructed a droid factory inside a lava lake deep within the mountain. It remained a closely guarded secret, hidden and for an unknown reason unused until after the end of the Clone Wars, when Gizor Dellso, a Geonosian leader traveled to the planet to meet up with the rest of the Separatist leaders.
Toward the end of the Clone Wars, it served as the headquarters of the Separatist Council. The Council members were slain there at the hand of Darth Vader. The slaying of the Separatist Council at the hands of Darth Vader transformed the area into a Dark side nexus, similiar to the Dark Side Cave of Dagobah.
The destruction of the factory.
The mining facility was abandoned and almost destroyed when it was host to the violent duel between Darth Vader and Obi-Wan Kenobi in 19 BBY. For two months it was not known what had happened to the members of the Separatist Council, as the new Emperor of the galaxy used the possibility of them still being alive as reason to continue bolstering the imperial military's strenghth. A salvage team eventually travelled to the facility and found the remains of the Separatist leaders executed by Darth Vader. Gizor Dellso was present during the discovery of his leader, Poggle the Lesser's body. Gizor remained at the facility, locating and re-activating a secret droid factory hidden within a mountain by the complex and managed to countermand the droid deactivation signal which he helped create, to enable him to build a new droid army. He also began work with other Geonosians on schematics for a prototype infantry droid.
The facility was eventually destroyed in the Battle of Mustafar when the stormtroopers of the Imperial501st Legion were sent to Mustafar to crush Dellso's droid uprising. They broke through the Separatist blockade, and, after placing an orbital strike beacon at a strategic point of the base, excecuted a Base Delta Zero order, pounding the factory into molten slag.