Key Largo, narrow island, c.30 mi (48 km) long, off S Fla., largest of the Florida Keys. Along with other Florida Keys, especially Key West, it has become an increasingly popular tourist spot, noted for its scuba diving, nightlife, and beachside resorts. Housing developments and shopping complexes have been recently constructed. A major attraction is John Pennekamp Coral Reef State Park, the first underwater park in the United States, containing c.78 sq mi (202 sq km) of living coral and hundreds of varieties of marine life. Also offshore is the Aquarius habitat, the National Oceanic and Atmospheric Administration's permanent undersea laboratory.