The Black Fortress is the home of the Beast, and an interplanetary spaceship/castle from The Beast's home planet. It lands on the planet Krull, unleashing its army of Slayers, and proceeding to take over the planet.
The interior of the Fortress is surrealistic, even dreamlike, and is composed of vast caverns, with bridges, secret passageways, and the room of The Beast, known as the Centre. The Beast can telepathically control the environment of the Fortress, manipulating passages, and creating traps for intruders, almost as if it is an extension of his body. The Black Fortress had been the Beast's home since leaving his home planet, and his base of operations in conquering the planets until Krull. Colwyn, and his friends, storm the Fortress to take backPrincess Lyssa. After destroying the Beast the Fortress is destroyed, and is forced back into space were it would become just meaningless asteroids.