These natural wells have been the only source of water for Yucatán farmers for millennia. Major Maya ceremonial centers were once constructed beside cenotes as are the indigenous villages that dot the landscape today. And when you consider the fact that these underground systems are old as the Sahara Desert (they were sealed off after the end of the last Ice Age about 10,000 years ago), the ancient Maya civilization seems strangely like recent history.Two thousand years ago, the ancient Maya were just as intrigued by caves and cenotes as we are today. Back then, these were sacred places where fervent Maya kings, and peasant alike, made offerings to their gods. Archeologists and cave explorers are only beginning to uncover what remains a vast unknown territory.A two-hour drive west of Cancún, imposing Chichén Itzá is worth the trip just to have a look at a real cenote. With an impressive 60-meter (197-ft) diameter, the perfectly circular Sacred Cenote is reputedly over 35 meters(115 ft) deep. Staring into its uninviting murky-green waters, it's easy to imagine the Maya's ancient rituals. The lonely remains of an ancient sweatbath stand nearby, conjuring up images of lofty Maya nobles preparing victims for sacrifice before abandoning them to the deep. Local folklore says that the cenote still claims a new victim every year, but this has never been documented.

Also in the vicinity is Cenote Zaci. Located right in Valladolid (on Calle 36), this strange dark cavern is worth a visit if you've never seen a cenote before. There's lots of otherworldly atmosphere here, although the stagnant green water is not recommended for swimming.Closer to Cancún, a vast series of underground treasures is ripe for discovery along what's known as the Riviera Maya. Aside from Caribbean beaches, quaint fishing villages and spanking new resorts, this 160-kilometer (100-mile)-long strip of coastline located south of Cancún is peppered with all kinds of cenotes, caverns and underground rivers.

Diving, snorkeling and cave exploring expeditions to some of the better known destinations are widely available and offer a chance to experience the strange geography that makes the Yucatán peninsula unlike any other place in the world.When it comes to snorkeling in an underground river or in a real cenote, Xcaret (72 kilometers/45 mi. south from Cancún) is a popular choice. With its underground tunnels and cavernous cenote, this privately-run park is a watery wonderland of bizarre treasures. Xcacel (119 kilometers/74 mi.) also boasts a good snorkeling cenote. Further south, there's Dos Ojos, about 122 kilometers (76 mi.) from Cancún and just past Xel-Há.Anyone trained in cave diving couldn't be in better place; more than 80 different cave systems have so far been registered in the Riviera Maya and more are being discovered every day. Among these, Nohoch Nah Chich (Maya for "big house of bird") recently made international headlines as the largest known underwater cave in the world. Divers at this awesome geographical phenomenon recently broke a world record covering more than 29 kilometers (18 mi.) of the uncharted system's interconnecting caverns and tunnels. The system is located a few kilometers from Akumal (about 104 kilometers/65 mi. south of Cancún).And what is it like down there? "You're visiting a very, very special environment", says Jim Cook, diver and scientist. "For one thing, the creatures living in the caves are far more fragile than humans. They have no eyes, no skin pigmentation, no real senses except for scent". About ninety-five percent of these cave dwellers are crustaceans, he adds, although you're also likely to see blindfish and the occasional eel.

The last time divers dredged the Sacred Well at the archeological site of Chichén Itzá in Yucatán, they came up with more than they bargained for. Skeletons of sacrificial victims, intricately carved jewelry and other, thousand-year-old offerings to ancient gods were all recovered from the well bottom.
You can expect to find just about anything in the uncharted cave system and natural wells that riddle the Yucatán peninsula. From the Caribbean shores of Cancún in the state of Quintana Roo, to the southeastern state of Campeche and the savanna landscape of the state of Yucatán, there isn't a single above-ground river. Rather, the flat limestone terrain of the north and central areas of the peninsula is crossed by a series of labyrinths, Caves and Cenotes (freshwater sinkholes caused by the collapse of cavern roofs). Rain is absorbed into the porous surface and passes through to underground rivers that connect the cenotes.The many underground rivers and extensive cave systems located near Cancún offer exciting opportunities for visitors interested in diving, snorkeling, cave exploration or just seeing one of these phenomena.

Just six kilometers (4 mi.) east of Chichén Itzá, the mystical Caves of Balancanché offer another intriguing link with the past. There you can take a 40-minute tour and see an immense cavern traversed by a several-hundred-meter-long path terminating in a stagnant pool.

Besides huge stalactites and stalagmites, you can also see dozens of ancient Maya metates (corn grinders) and ceremonial artifacts left behind by anonymous worshippers when they abandoned the cave about 800 years ago. Just who those ancient visitor were and why they hastily departed the caves is something that's been contemplated since 1959, when a local guide discovered the caves when he pushed against a cave wall, causing it to suddenly give way.Another amazing geographical phenomenon is Cenote Dzitnup. Located just outside the colonial city of Valladolid (about a two-hour drive west of Cancún) this fantastic natural cave is one of the most dramatic of its kind on the Yucatán peninsula. Clambering down a rock-hewn staircase, you suddenly find yourself in a vast cavern, right at the edge of the cenote. Sunlight filters through a small opening in the cave roof giving the still blue water an unearthly quality. An impressive gallery of stalactites and stalagmites completes the scene. Sun-baked visitors inevitably opt for a refreshing swim in the chilly waters and are encouraged to do so.

Cook has personally done over 2,500 cave dives and has made all kinds of fascinating discoveries, not the least of which included archaeological relics left behind by Maya explorers in search of fresh water source thousands of years ago.Needless to say, exploring an uncharted cave is a dangerous undertaking. "Unlike open water (e.g. reef) diving, there is no direct access to the surface, so it really makes no difference whether you're three kilometers (2 mi.) into a cave or a mere 45 meters (150 ft), the dangers are just as intense", he says. To avoid complications and dangerous situations, divers bring backup lights, and they also lay guide lines—absolutely essential since the slightest disturbance of silt in the caves can instantly reduce visibility from hundreds of yards to mere inches. As well, he says, there is a mandatory air rule: save two thirds of your air for the journey back. A simple but effective precaution.For any advanced diver interested in doing a cave dive, Cook recommends consulting a reputable dive shop that specializes in this special kind of diving. Check out those in Akumal and Puerto Aventuras; their teams are experienced", he says.Non-divers can also experience this underwater world. Because cenotes are usually entrances to vast cave systems, it is possible to do a little snorkeling in the area. At Nohoch, a large cenote and 106 meter (348-ft)-long, open-air tunnel allow for some amazing snorkeling for even the most inexperienced.