Zaci – in Valladolid Located in the heart of Valladolid, this is a semi-open cenote. It has a diameter of 150 feet and a total depth of 260 feet. This is a popular cenote for swimming in the refreshing turquoise waters. One third of the cenote is covered with stalactites and stalagmites. There is a walkway around the entire cenote.
Swimming in Cenotes (Mexico) 'An estimated 6000 cenotes (limestone sinkholes) dot the peninsula; some, like the spectacular pair of caverns at Cenote Dzitnup, make for refreshing, fun-filled swimming holes, while others, such as the underground cave system at Dos Ojos, draw divers from far and wide.' http://www.lonelyplanet.com/mexico/travel-tips-and-articles/76195