St. Augustine Castillo de San Marcos

Built by the Spanish in 1672 and never taken by military force, this coquina stone fortress has held pirates, rebels, and Native American leaders as prisoners — including Osceola, the Seminole leader who died in captivity at Fort Moultrie after his capture here. Soldiers have been reported standing at attention in period Spanish armor along the ramparts. Two skeletons were discovered mortared into a wall during 1833 renovations, and the sealed room where they were found remains one of the fort's coldest spots.