CHICHÉN ITZÁ, MEXICO—Scientists from Mexico’s National Autonomous University tell the Guardian that they have discovered a subterranean river under El Castillo, the main pyramid at the Maya site of Chichén Itzá. The river was identified about 60 feet below the pyramid using geophysical techniques, and may have once connected some of the sacred sinkholes, called centoes, that surround El Castillo. To read about the discovery of a famous ancient pigment at Chichén Itzá’s sacred cenote that made our Top 10 Discoveries list, go to “Sacred Maya Blue.”