Dry Tortugas National Park
Also called the "Gibraltar of the Gulf," construction on Fort Jefferson began in 1846 at the western end of the Florida Keys to protect the Florida Straits. It is the largest all-masonry fort in the western hemisphere, which served as an important Union military post and prison during the Civil War. At one point it was home to some 2,000 occupants, including soldiers, their families, laborers and prisoners. In July 1865, Fort Jefferson received its most infamous prisoners when four men convicted for conspiracy in the assassination of President Lincoln were imprisoned there, including Dr. Samuel Mudd, the Maryland physician who had set the broken leg of John Wilkes Booth. As one of the most remote parks in the national parks system, Fort Jefferson is accessible only by boat and seaplane which depart from Key West, 70 miles away.