The Fortress of the Self-Referential Six is a giant fortress located within the Meta Reality and the residence of the team, the Self-Referential Six, which Rick and Morty visits to take Previous Leon to them. Within the fortress, the two fight all of the members of the team and free Rhett Caan, who has been previously imprisoned by the team. Rhett Caan has currently transformed the entire fortress into a giant orange. It first appears in "Full Meta Jackrick".
Rick and Morty Wiki