Located on a spur of high ground overlooking the River Fowey, Restormel Castle is an unusually well-preserved example of a circular shell keep, a rare type of fortification built during a short period in the 12th and early 13th centuries. Only 71 examples are known in England and Wales, of which Restormel Castle is the most intact of all. Such castles were built by converting a wooden motte-and-bailey castle through replacing the external palisade with a stone wall and filling the internal bailey with domestic stone buildings, clustered around the inside of the wall to form a defensive bailey; the buildings are curved to fit into the shell keep, in an extreme example of the 13th-century trend.