The Florida Keys are surrounded by the planet's third-largest barrier reef, which belongs to the Florida Keys National Marine Sanctuary (floridakeys.noaa.gov). The reef harbors more than 6,000 plant and animal species, including five types of marine turtles and the endangered Florida manatee. Book a dive or snorkeling trip with a vendor that has received Blue Star certification, which recognizes commitment to reef conservation. The region is also home to bottlenose dolphins. For a chance to see them in the wild, enlist a local tour operator that participates in the Dolphin SMART program, which encourages viewing in ways that are not disruptive to the animals. Alternatively, you can swim with dolphins and sea lions at conservation facilities such as the Dolphin Research Center (dolphins.org) in Marathon. Other "green" attractions here include the Key West Tropical Forest & Botanical Garden (kwbgs.org).