Cenote Zací is downtown between calles 34 and 36 and calles 37 and 39 (Mex. 180), about 3 blks. e. of the main plaza. This huge underground sinkhole is reached by worn stone stairs that descend to a dark, spookily atmospheric cavern, with upper walls populated by bats. The somewhat murky water is suitable for swimming but is flecked with green scum that the locals call “lake lettuce.” It is located in a park that has a restaurant as well as examples of traditional thatch-roofed Mayan houses.