"Dry Tortugas, a national park that exists primarily over open water, is home to incredible marine life and birds, and visitors can camp, dive, snorkel, and swim. This is one of the least-visited national parks in the country, meaning that everything you can see and do is pretty special—no dodging selfie sticks. Standouts, however, include Port Jefferson, built as a line of defense following the War of 1812, and the Windjammer wreck site, where experienced divers can get close to the wreckage of an early 20th-century iron-hulled ship." - Nancy DePalma , Laura Ratliff