Castle Martorius

Decades after the Gods' End, an enormous palace of shining, opalescent towers and silken banners appeared atop a mountain overlooking Abendland. The castle's owner is the archmage Martorius. He claimed that he had lived on this land before The Burach Empire even existed, but had spent the intervening years traveling between dimension in pursuit of his magical research. Now, he assured the Unterland folk, he had no interest but to observe developments in the Empire as they unfold.
Indeed, the archmage's castle is a wonder to behold. Dignitaries that have visited it report there is no way to determine its true dimensions, as it expands and adds rooms to itself as necessary.