Fort Pickens, Gulf Islands National Seashore, Santa Rosa Island, Florida, USA.
After the War of 1812, the United States decided to fortify all of its major ports. Fort Pickens, on the western tip of Santa Rosa Island, was the largest of a group of forts designed to protect Pensacola Harbor. Construction lasted from 1829 to 1834 with black slaves laying most of the 21 million bricks.
During the Indian Wars, Apache war chief Geronimo was imprisoned in Fort Pickens along with several of his warriors.
The fort remained in use through World War II until 1947. It's now part of the Gulf Islands National Seashore and is administered by the National Park Service.