One of the greatest marvels of the marine world, the Belize Barrier Reef runs 190 miles along the Central American country"s Caribbean coast. It"s part of the larger Mesoamerican Barrier Reef System that stretches from Mexico"s Yucatan Peninsula to Honduras and is the second-largest reef in the world behind the Great Barrier Reef in Australia. Declared a UNESCO World Heritage Site in 1996, the Belize Barrier Reef has remained relatively healthy even as many of the planet"s reefs are threatened by climate change.