Cenote is the Mayan word for the deep
water-filled sinkholes that the ltza associated with the underworld. Since the soil and
rock in the region is porous and does not hold water well, the eerie underground pools had both practical as well as religious
meaning. Of the two in the city, the southern one was used for drinking water, and the northern one, connected to the surface by
a ceremonial path, was used for sacrifices. The structures around the southern cenote are the older ones. Here, the main structure is the Caracol, or observatory. A circular structure on a trapezoidal base (that is itself raised on a large rectangular platform), the concentric walls of the Caracol have tiny openings that align to track the movement of various stars and, in particular, Venus.