The Fortress of Doom was part of Tom Paris' The Adventures of Captain Proton holo-programs. Accessible by a drawbridge and underground caverns, the fortress contained many of Chaotica's evil inventions and henchmen. It was protected by a lightning shield, which made infiltration by even Captain Proton quite difficult. The lightning shield failed to protect the fortress, allowing it to take heavy damage when the appearance of photonic lifeforms caused the program to be left on continuously, setting off a war between them and Chaotica. (VOY: "Bride of Chaotica!")