Un Cenote Lindo, Yucatan, Mexico
A bather wades in clear blue waters in a cenote, or sinkhole, on the Yucatan Peninsula of Mexico. Cenotes form when the limestone ceiling of a cave collapses, revealing the void (and the groundwater) below. Some of these sinkholes look like large exposed lakes, while others, like this one, become underground cathedrals, with only a small hole in the ground allowing rays of light through. The water in cenotes is crystal-clear because it percolates up through the ground, carrying with it very little suspended sediment.
(via: Live Science) (image: Samiksha Volvaiker)