Dry Tortugas National Park

Dry Tortugas National Park preserves Fort Jefferson and the Dry Tortugas section of the Florida Keys. The park covers 101 mi² (262 km²), mostly water, about 68 statute miles (109 km) west of Key West in the Gulf of Mexico.
It is famous for abundant sea life, colorful coral reefs and legends of shipwrecks and sunken treasures. The park's centerpiece is Fort Jefferson, a massive but unfinished coastal fortress. It is the largest masonry structure in the Western Hemisphere,[1][2] and is composed of over 16 million bricks. The park plays host to almost 80,000 visitors each year. The park is accessible only by seaplane or boat. Activities include snorkeling, picnicking, scuba diving, saltwater fishing and birdwatching. (from: wikipedia)