The Black Sun fortress was a heavily defended structure constructed within the cliffs of Mustafar, a planet with volcanic activity located in the Outer Rim. From this location, a group of Falleen nobles, forming a cabal, directed the activities of the criminal organization known as the Black Sun throughout the Clone Wars period and afterwards. This was the location where Maul and the Death Watch Mandalorians confronted the heads of Black Sun, demanding they become part of the Shadow Collective, a criminal enterprise established and controlled by Maul. Even though Black Sun left Mustafar during the Galactic Empire's reign, the fortress saw continued use in the New Republic Era. Maz Kanata, the Pirate Queen, mentioned the fortress in her journal, noting it as the place from which the Black Sun leaders managed their syndicate.
The Black Sun fortress initially appeared in "Eminence," which is the fourteenth episode of Star Wars: The Clone Wars's fifth season. While the facility wasn't explicitly named in its initial showing, the official episode guide confirmed its identity as the Black Sun fortress.