Senyakhaz's Mirror is a portal of some description used by the fell sorceress.
It was known to transport people to many places both near, such as within the same castle, and far (for instance Arion, the Wastes of Chaos). Even, some say to a distant planet where the moon shines in such a way as to be reminiscent of cheese. It also transports through time. It is not a device to be used by the unwary.