Halfway between Florida and Cuba in the Gulf of Mexico lies the remote Dry Tortugas National Park. The 100-square mile park is mostly open water with seven small islands. Spanish explorer Ponce de León gave the Dry Tortugas their name on his first visit in 1513.
Fort Jefferson is located on Garden Key, the second largest island in the Dry Tortugas. Construction of the fort started in 1846 but was never completed. For some time the fort served as a prison.