Last Wednesday, after ten months of work, the Underwater Exploration Group of the Great Maya Aquifer Project (GAM) found a connection between two of the most extensive flooded cavern systems on Earth—Sac Actun and Dos Ojos, both in Mexico's Yucatán Peninsula—now forming the world's largest known flooded cave, with a length of 215 miles.

"This immense cave represents the most important submerged archaeological site in the world, since it has more than a hundred archaeological contexts, among which is evidence of the first settlers of America, as well as the extinct fauna and, of course, of the Maya culture," says Guillermo de Anda, a National Geographic explorer and director of the GAM.

This phase of the project began in March