Pevensey Castle
Starting life as a Roman Saxon shore fort around 290AD, a fortified keep was constructed in the walled perimeter by the Normans after the invasion of William Duke of Normandy in 1066. The end of the 16th century saw the castle crumbling to ruin until it became state owned in 1925.
Fortified during WWII with machine gun posts, which still exist today, the castle with its keep, gatehouse, dungeons and resident ghost, is an intriguing place to visit. Owned by English Heritage you can walk through the old fort grounds for free.