Castle Grayskull is a fictional fortress and castle featured in the Masters of the Universe multimedia franchise. It first appeared in a series of mini-comic books, which were included with the series one Masters of the Universe action figures by Mattel.
Castle Grayskull is located on the planet Eternia and its sole occupant is a woman known as the Sorceress. The castle itself was bound to the Sword of Power, which had been split into two halves, one of which was used by Prince Adam, and the other was wielded by Skeletor. Skeletor always sought to unite the two halves and take control of Castle Grayskull. To invoke the mystical power bestowed by the enchantments placed on the castle, Prince Adam would hold the Sword of Power aloft and speak the words, "By the power of Grayskull... I have the power!"