Cacahuamilpa caverns. It is an underground cave system, still active (which means water still filters through) that was formed 85 million years ago. It is home for bats (though we didn't see any) and lays 450 m. "inside" a mountain. The highest "hall" is 81 meters tall. It really was an impressive sight, after all it is the 2nd largest cave system in Latin America. (If you are wondering, the World's biggest is Son Doong, in Vietnam). The national park and cave was discovered in the mid 1800's, though, interestingly, it had been used for religious rites by the Olmecs and Chontals and diverse pottery objects were found. If you are ever around and enjoy adventures don't miss it.