1) Deep well used in Mayan rites 2) Natural underground reservoir 3) Well used by Mayans 
deep natural well
(from Maya dz`onot), natural well or reservoir, common in the Yucatán Peninsula, formed when a limestone surface collapses, exposing water ... [1 related articles]
a deep natural well or sinkhole, esp. in Central America, formed by the collapse of surface limestone that exposes ground water underneath, and sometimes used by the ancient Mayans for sacrificial offerings.