Castle Grayskull is a fortress located on the planet Eternia. It forms a central location in the Masters of the Universe comic/animation universe, and also appears in the 1987 live action adaptation. In the series, it is the target of numerous attacks by Skeletor, Hordak and the Snake Men, all of whom believe that the secrets inside will allow them to conquer Eternia and become the titular masters of the universe. During the Great Wars and until the reign of King Grayskull, Castle Grayskull was also a center of religion, particularly the worship of Eternia's Goddess.