Cenotes of the Yucatán
The underground river systems of the Yucatan flow beneath the entire peninsula. During the ice ages when the ocean levels were much lower than they are today, what was once a giant coral reef became exposed to the atmosphere and eventually became the Yucatan Peninsula. Massive cave systems were formed by gradual dissolving of the highly porous coral limestone. These caves are called "solution caves" because they were formed by the slightly acidic rainfall dissolving the alkaline limestone. Inside the caves the geological formations such as stalactites and stalagmites are a spectacular sight to see. Many of the caverns eventually collapsed and the sea levels rose partially or completely flooding the cave systems. The water table of the entire peninsula is filled with consists of seawater at sea level and freshwater 'floating' on top at varying depth depending on the distance from the sea. For instance, Cenote Zaci in Valladolid in the central Yucatan area is about 35 metres from ground level to the surface of the freshwater and probably another 30 metres below that would be the top of the saltwater layer.
It has been estimated that there are approximately 30,000 cenotes or exposed access points to these cavern and cave systems and thousands of miles of underwater cave passageways have already been explored and exploration continues in too many systems to count. Two of these cave systems have over 140 km of explored passages.
Cenotes are complexes of sinkholes and caves in the Karst geological landscape of the Yucatán. Some cenotes contain spectacular cave formations, while others are important archaeological sites, and several were considered sacred by the Mayans. A few are open to the public for swimming and diving. Of the estimated 30,000 cenotes, many of them unexplored, many are considered to be Mayan cultural and archaeological sites. Ancient fossilized remains of Camels, giant Jaguars and Mammoths are among the interesting archaeological finds in recent years. Most of these have been found by cave divers exploring underwater cave systems and some sites are now protected by INAH, the Mexican government archaeological and historical protection organisation.
Tour operators emphasize the sensitive nature of cenotes, and La Ruta de los Cenotes was first promoted as an ecotourism attraction that would offer sustainable development for the region. To promoters in Quintana Roo, it was a way to bring tourist revenue to a relatively forgotten and marginalized part of the Mayan Riviera. However, some Mexican environmentalists have criticized the construction of the eastern segment of the highway, both for the destruction of pristine forest lands and for the use of heavy equipment in sensitive areas.
Recently, experienced divers have discovered Maya artifacts upsteam of some of the sinkholes they explored dating back over 1,000 years. This has led them to conclude that the water table in this area was significantly lower at one time and the Maya inhabited the caverns which are now full of water. They also concluded that some of the sacrifices made, were to ask the spirits to lower the water table so that they could resume life in the caverns. They also believed that the Maya remained in the area for some time living above ground, while waiting on the waters to recede, before moving on.
Formed during the Ice Ages, the cenotes were held sacred by the Mayan Civilization and many contain remains of offerings to their gods.
Holes in the rock from the size of small crevices to giant openings over 100 M across. In most areas of the peninsula, the cenotes are the only open fresh water to be found.
 Flora and fauna
Many animals rely on the cenotes for their fresh drinking water. Many others make their homes in and around them including many endemic species including blind cave fish and blind crayfish which live in areas where light never penetrates.
Tropical semi-dry jungle and forest.
Some cenotes are privately owned while others are run by local Mayan communities such is the case of Yokdzonot Cenote nearby Chichen Itza; if you go, they will provide you with a safe vest for a small fee. Yokdzonot Cenote and Ecological Garden should not be missed, the water is pristine blue, the place clean and well kept by a group of Mayan local females that built their own open restaurant and palapas on site, with clean public bathrooms and an eco-friendly water waste system that contribute to the care of the environment and the pride of the town.
 Get in
By land from Belize, Guatemala and all points south and by road from there. By plane into Cancun or Merida airport.
Many are located on private land and accessible only with permission. Most are basically inaccessible by normal means but dozens are open to the public. Entrance fees vary from $10 pesos to $100 pesos (roughly US$1-10) for cenotes managed by locals. Commercial operations will charge more, US 10-25, usually with more to do or see.
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Parts of the route are unpaved. It is listed in Spanish touring guides as a corredor turístico, and is marked in a number of places. At the eastern terminus on Highway 307, there is an archway constructed of concrete. Most of the route was laid out over existing secondary roads. The name is used locally in Quintana Roo for a newly constructed road segment that connects Puerto Morelos with the interior. As of early 2008, 16 k are paved, in from Puerto Morelos. From there the road is not for fast travel.
Note that there are numerous cenotes along Hwy 307 south of Playa del Carmen, as well as those on the road out of Tulum towards Cobá.
 Stay safe
Lock your doors and be careful of cenotes where there is no supervision or where the parking areas are remote. People have had their cars broken into and all their clothes, money etc. taken.
 Get out