Poço Azul, Chapada Diamantina, Brazil
Found inside the Chapada Diamantina National Park, the Poço Azul (which translates as Blue Well), is an underwater cavern that is between 50 and 60 feet (15 and 18 meters) deep. The water supposedly stays warm throughout the year and is so clear that, during some parts of the day, swimmers seem to be floating in air.