The mystic castle that served as the Mystical center of Eternia. according to the cartoon, by Filmation, It served as the home of the Sorceress. however in the comic book that was included with the figures it was said that Castle Greyskull could only be open when the swords of He-man and Skeletor were joined. thus a small crevis as well as a outcroping of plastic were molded into the swords.