The impressive heap that is Richmond Castle, founded in 1070, was one of the first castles in England since Roman times to be built of stone. It's had many uses through the years, including a stint as a prison for conscientious objectors during WWI (there's a small and sobering exhibition about their part in the castle's history). The best part of a visit is the view from the top of the remarkably well-preserved 30m-high keep, which towers over the town.