Fort Jefferson, Dry Tortugas National Park
Key West, FL 33041, USA
Website: www.nps.gov/drto »
Once known as the "Gibraltar of the Gulf, " Fort Jefferson is the largest all-masonry fort in the Western Hemisphere. It was garrisoned by Union troops throughout the Civil War and also served as a military prison. Dr. Samuel Mudd and three Lincoln assassination conspirators were among those imprisoned at the fort.