Fort Delaware

A granite and brick fort on Pea Patch Island in the Delaware River, built to guard Philadelphia and used in the Civil War as a prison camp. It held up to 12,500 men in space meant for a fraction of that; around 2,500 died, mostly of disease, and are buried across the river at Finn’s Point. Given that history it has the reputation you would expect, and the state runs lantern ghost tours. The fort itself is extraordinary masonry and reached only by ferry. PUBLIC state park.