Castle Gnome is a castle on the top of Mount Gnomalia, across from Fortress Mountain. It is one of the oldest buildings in all of Gnomalia, and serves as the headquarters of the Gnomalian Alliance.

The Castle was built in a rectangule shape, topped by a typical slanted roof. In front were three main towers, followed by some more minor towers, while the two right towers were connected by a long bridge. The castle was divided into two parts: the entrance hall and the dining hall, connect by a great staircase. The dining hall contained a seat for each Gnomalian representative, whether it be a secretary or the leader themselves. At the front was an emerald-cased throne for King Justin I, and to the sides a ruby one for May and a gold one for Brandon. Later, the three would sit in seats equal to the others, with the thrones remaining as a historic piece.