Restormel Castle

If you want to understand what a shell keep is, this is the one to see. Instead of a square tower, a ring of stone wall was built around the top of an earlier earth mound, the motte, raised around 1100, with the main rooms fitted within an almost perfectly circular plan. The national listing calls it one of the most intact of all known shell keeps, and its walls still stand to the height of the wall walk, so you can circle the whole ring and look down over the earthworks below. It is a quiet site in the Cornish countryside, and it shows the stage between earth-and-timber castles and full stone fortresses better than almost anywhere else. It changed hands twice during the English Civil War, in 1644.