Dry Tortugas National Park

This national park is the only at-sea national park in the United States of America and is home to the historic Fort Jefferson. The park is located about 70 miles (112.65 kilometers) west of Key West and is accessible only by boat or chartered seaplane. The park and fort lure divers, snorkelers and nature lovers from all over the country who flock here to get a closer look at the highly-endangered staghorn coral, angelfish, rare birds and the loggerhead turtles that gave the island its name. Built in 1846, the five-sided fort covers more than 11 of the island's 16 acres (6.47 hectares). The fortress was never finished but when construction stopped, records showed that 16 million bricks had been used to build this monolith of a building. The park is also an integral component of the UNESCO-certified Everglades & Dry Tortugas Biosphere Reserve.