Underwater underground

Like a giant block of Swiss cheese, Mexico’s Yucatan Peninsula is riddled with holes called cenotes. Cenotes form when subterranean limestone dissolves, allowing underground water to penetrate. The rock above may cave in, forming a pit and revealing the cool, often crystal-clear water, while other cenotes may remain hidden and unexplored. Cenotes vary in size from very small to several dozen yards across, and recent discoveries have shown that cenotes lead to a series of underground cave systems that can span several miles in length.
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