The Hall of Mirrors, in the Caven of Doom region, is a huge underground cavity with a gigantic magical mirror filling the far end of the room. As there was a strange link between this cavern and the Castle of Zork, the image in the mirror displayed an exact backwards replica of the banquet hall of the Castle of Zork. Like most magic mirrors, touching the surface would teleport one to the location in the image.

A similiarly functioning Hall of Mirrors is also to be found within Largoneth Castle.

SOURCE(S): Zork Quest III:The Cavern of Doom, Enchanter