Castle Grayskull
From superman.nu: Supermanica
Castle Grayskull
Located in Eternia, Castle Grayskull is a castle containing "hidden secrets," secrets that are sought after by the villain Skeletor. Skeletor plans to gain access to the castle by combining the magicks of two ancient power swords, "for whoever gains possession of its secrets shall rule Eternia" (DCCP No. 47, Jul 1982: "From Eternia--with Death!").
At present, most of the castle's power seems to be under the command of the "mighty Sorceress," her authority and honor guarded by He-Man and the Masters of the Universe.