Explorers have found a connection between two underwater cave systems in Mexico's Yucatan Peninsula, making it the largest known underwater cave in the world.  The 215-mile system consists of the San Actun and Dos Ojos caves, among others, and contains a remarkable amount of biodiversity.  It also contains archaeological evidence of the Mayan civilization.  

The discovery comes after 20 years of extensive probing of the cave systems.  The connection was verified  last Wednesday.

Photo: AOL