Fortress Vader, also known as Darth Vader's castle, was a stronghold located on the volcanic world of Mustafar. Once the site of a Sith temple, the fortress was built above a Sith cave that still remained, as well as the ancient Corvax Fortress located underneath. The castle was designed by the preserved consciousness of the ancient Sith Lord and artist Darth Momin, whose haunted mask possessed an Imperial lieutenant and made him create the fortress's blueprints. The castle came to serve as Vader's personal residence and from time to time, he healed and rested inside a bacta tank.