![](https://thehollowearthinsider.com/blog/wp-content/uploads/2013/05/RiverExitTolantongo-CREDIT-Thelmadatter-SOURCE-Wikipedia-Commons-Public-Domain-112x150.jpg)
Featured Image: Karst cave with underground river exiting at Tolantongo, Hidalgo State, Mexico. CREDIT: Thelmadatter SOURCE: Wikipedia (Public Domain)
From youtube uploaded by journeymanpictures
Published on Apr 29, 2013
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