Visit Dry Tortugas National Park, the end of the line in the Florida Keys, for a spectacular ride back in history. Accessible only by boat or seaplane, the Dry Tortugas, 70 miles west of Key West, harbor a rich history and an even more prolific underworld. You’ll be able to take a self-guided tour of Fort Jefferson on Garden Key, America’s largest 19th-century coastal fort, which was started in 1846 but never completed. For years the fort operated as a military prison. The protected waters surrounding the Tortugas sparkle with all the sea creatures of the coral reef as well as a good many shipwreck remains. With natural sand beaches and calm seas, snorkeling and swimming are a must.