Archaeologists are hoping to discover an underwater cavern hidden beneath the imposing "El Castillo" temple, at Chichen Itza, Mexico.
Chichen itza, in Yucatan state, is one of the most impressive achievements of the ancient Mayan people. Pictured, thousands of tourists surround "El Castillo" during a spring equinox celebration.
Water-filled caverns -- called cenotes -- sustained the Mayan civilization, and were central to its spiritual beliefs. Pictured, Holtun cenote in Chichen Itza.