8. Castle Williams was Both a Prison and Community Center
Castle Williams, on the west point of the island, stands as a circular defensive structure made of red sandstone. Constructed between 1807 and 1811, it was considered the prototype for modern fortifications. It served as a prison during the Civil War and again in 1903.
In 1966 when the Coast Guard wanted to demolish it, the castle was remodeled as a youth community center. Its prison cells were converted into nurseries, meeting rooms for Scouts and clubs, a woodworking shop, art studios, a photography laboratory, and a museum. Today the historic site is run by the National Park Service.