When you do your first teleport in the rift, you probably came out to the area that leads to the castle courtyard. That is near a set of large doors witha gargoyle on top - use the stone there. To get the stone, teleport back, then choose the other path to teleport (there are two teleporters side by side). That will lead you to where you use the "sanctum key" to get to the fight for the beckoning stone. This is also the path to use the "flamequencher wand" to get the "staff of ash".
Tools for Wizardry(r) 7