Found in only a few regions of the world, cenotes are sinkholes containing groundwater--many also have caves. The cenotes of the Yucatan are particularly renowned for their rich cultural history. Performing rituals alongside the deep pools, the Mayans sacrificed both humans and treasure into the depths. Millennia later 19th century explorers dredged the bottoms for those hidden riches. Today visitors enjoy escaping hot days by diving into the cenotes.