Riverrun is the seat of House Tully. It is a large castle located in the central-western part of the Riverlands. It sits at the point where the Red Fork of the Trident Riveris joined by its major tributary, the Tumblestone River flowing out of the west. In times of danger, sluice gates can be opened to flood a channel cut to the west of the castle, turning Riverrun into an island. Its walls rise sheer from the waters and its towers command the opposite shores, making assaulting it almost impossible without huge casualties.
In the A Song of Ice and Fire novels, Riverrun is a triangular castle made of sandstone. It is located at the confluence of the Tumblestone River and the Red Fork of the The Trident River.
Riverrun has been in the possession of House Tully for a thousand years. It became the seat of rule over the region when House Tully rebelled against the ironborn occupiers and allied with Aegon the Conqueror three centuries ago.