The Cenotes.
Lets start by defining the word cenote.

A cenote is an opening on the jungle's limestone rocky  floor. The opening is generally circular , but it may look like a short river or lagoon. There are six configurations for cenotes, the vase, the cave , the stream, the pond, shown in the picture below, the submarine and  the lagoon. The sections of a cenote are , the edge, the neck , the water mirror, the cave entrance, the submarine chambers the channels and the tunnels. There are various depths in the cenotes configurations. The deepest ones are the vase and the cave types. The ones at ground level are the lagoon type and the stream types. A vase type cenote the picture below.

Chichen Itza. is a  good example of a vase type cenote It is deep and the mirror of water is in the bottom. There are trees growing from the bottom of the vase of the cenote in the border of the mirror of water. This trees are very tall and the top of the trees exceeds the border of the vase of the cenote. When this happens the cenote is disguised by the tree tops greenery. You can be walking in the jungle and not notice it. Chichén Itzá was a great Mayan city, in the Yucatan Peninsula. One of the most showy things of this city is the impressive Sacred Natural well where it thinks that the Mayans threw virgins as offering to the God of the water. In fact Chichén Itzá means "Mouth of the Well of Iztá or the Wizard of Agua". From the well-known main structure as the Castle arrived traverse from sacbé or white way to this impressive natural well that measures 62 meters of circumference almost vertical average and its walls they have a height of 22 meters. From the surface of the water to the bottom the maximum of depth is of 13,4 meters. The visibility with natural light is until the 2,40 meters and to this depth one can as soon as to distinguish objects located to a meter of horizontal range. Of the 2,40 meters to the 4,20 meters the dark is something of luminosity beyond the 5 meters is absolute. The first attempt to recover the pieces of the Sacred Natural well of Chichén Itzá was the one of the French antique dealer Desiré Charnay, in 1881 or 1882, but without no success. It was Edward Thompson, first consul of the United States in Yucatan thatI carry out the second rescue operation in two seasons, from 1904 to 1909 and from 1910 to 1911. Thompson used a dredge because the little visibility of the water prevented them to dive with diving apparatus. He obtained pieces of jade, gold, , obsidian, masses of copal, skeletons, and even textile pieces, all that finished in the Peabody Museum of the University of Harvard. The fact to have removed from the country the mayan pieces led the government of Mexico to demand Thompson years late. This was known as the Thompson case. Its case contributed to seat the precedents to develop a legislation of protection to the rest of the past in our country. The National Institute of Anthropology and History participated for the first time in a project of excavation in the Sacred Natural well of Chichén Itzá in the 1960-1961 along with National Geographic Society and the Club of Explorations and Aquatic Sports of Mexico (CEDAM). These works were suspended in 1967 when the Dr Roman Chán directed the project. The procedure was to pump the water of the natural well and to clarify it with chemical agents. The water that was extracted happened through a mesh where they were left the pieces sucked and in the parts of the bottom which they were in the open they made excavations "in dry". Of these works they recovered around 100 vases, gold articles, worked rock, jade, crystal, obsidian, in addition to fragments of textiles, human copal, rubber, coral, shells, amber, quartz, pyrite, onyx, bones and of animals. A Peculiarly of the study of the bones showed that the women were not most of the sacrificed people The archaeological works in this natural well represent the important antecedent but for Subaqueous Archaeology because in them I am clear that it is not possible to study the objects in his context if they are extracted of the bottom of the water without a subaqueous technique specialized and a methodology that allows us to interpret them. For that reason the dredged one of the natural well was suspended.

Another vase type cenote
A few kilometers of Chichén Itzá, towards the north, is the Natural well of the Sacrifices, sacred place where human lives were offered to the Gods. Chichén Itzá, is one of the more impressive  Mayan archaeological sites and better known. The old Mayan world attracted the attention of travelers and students, like Brasseur de Bourbourg and John L. Stephens in century XIX, that arrived at the Yucatan Peninsula and the North region of Central America attracted by the fascinating secrets of a strange and seductive culture. By its origin and fusion of originating cultural elements of the center of Mexico, of the south of Central America and the own Mayan region, Chichén Itzá (' Mouth of the Well of Itzá', the city of great Lord Kukulcán), became the more important archaeological place during many years. This revaluation had its period of greater height thanks to the works of Sylvanus Morley and its outstanding team of archaeologists: Earl Morris, Alfred Tozzer, Karl Ruppert, George C. Vaillant and J. Eric S. Thompson, whose works, from 1924 and the subsequent years of that same decade, allowed the reconstruction of the Temple of the Soldiers, the Observatory and several structures more. But in previous date, between the years of 1904 and 1907, Edward Thompson - somewhat romantic trader, because it believed to have rescued, between valuable jewels, the bones of many virgins -, managed to reunite an impressive amount of archaeological objects: worked ornamentals gold slopes, plates, masks, ring and figures, as well as mud censers, bells and pitchers fine. This extreme treasure around thirty thousand pieces, pertaining to the Peabody Museum of the University of Harvard, institution that sponsored the works of Edward Thompson. An ample interpretative sample of these Mayan treasures crossed several museums of the United States and Canada in 1987, after more than seventy years in which these pieces jealously remained kept. By means of this traveling exhibition and of a catalogue that accompanied it in its route it presented the world for the first time this archaeological treasure coming from the Natural well Chichén Itzá.

This is a pond type cenote.

On the way to the tixbacab cenote the jungle was a little thick but not to the point of needing a machete to cut trough. It was thick enough to not been able to see ahead more than 30 feet away and some times even less. The jungle floor was rocky from time to time but not slippery. As while walking one has to be looking at the floor to watch where to put feet the attention to the things ahead is less. Suddenly the guide ahead stop, only jungle around us. Then the guide seem to disappear down the jungle leaving me alone in the rocky trail. He disappeared 30 feet ahead of my  position. I could not see more than the green thick jungle. Continuing advancing following the trail I reached a point in which I could see trough the jungle bush what seemed to be a clear. I had to put apart the bush to enter the clear area , when I did it and took the step forward to the clear I was looking down as it was more rocky here. When I finished the step and raised mi view a striking marvelous view was in front of my eyes it was a giant hole with walls that dropped flat down to a huge water mirror.  I ended up standing at the very stone border of a cliff . the cliff was the border of a vase 100 feet deep and 400 feet wide in a perfectly circular shape. The water at the bottom of the vase was clear and looked clean, small fishes and turtles swimming in the water. I was out of my breath for a while and a sensation of being in the presence of something very special. Flocks of parrots and other birds flying in circles in the inside of the vase of the cenote where drinking from the mirror of water and fly up in circles to leave the cenote. Bats coming out of small caves in the stone walls to start their night hunting. Small deer coming down to drink. It was such concentration of life it make me feel very impressed not believing what I was looking into and humble looking at this magical sight. There is a no rivers land and several animals only have this option to drink. After a while of observation in this position at the top of the base we start descending the cliff following a path in the rocks that looked like a stair. This may have centuries of use by the ancient inhabitants of this region. Once at the bottom there where the trees growing up , some guy climbed one and took a dive into the water mirror from a tree branch. It is a special feeling to be in the bottom of this vase. The walls are pure rock and completely vertical. Some cactus grow out of the walls and there are bromeliads and other plant species adapted for this environment. May be the evaporation of water is enough to produce the humidity necessary for this cactus to survive.  The water mirror was dark and the water was clear. The water is so quiet , the bottom cannot bee seen . There was big a tree floating in the water the water was very fresh, in the jungle heat is a very refreshing sensation. Some native Mayan children use ropes tied around their waist and to a tree. They jump into the water and use the rope to pull themselves back out of the water. This kind of cenote offers the chance to practice sports as rappel, rock climbing, diving, snorkeling and scuba diving.One of the most awesome views is the one of a big and deep cenote in the jungle. Some years ago I was part of a group bringing help to the town of tixbacab. The only thing to see there was the town’s cenote.

The cenote at TanKah is located 6 kilometer from Tulum going in the direction of Cancun. This is a very beautiful stream like cenote. The stream is 1,000 feet long and is like a elongated pond at ground level, it is not sunken. The water at the tan Kah cenote are extremely clear, The bottom is white sandy , the mangrove roots form underwater canopy under colorful fish hide.  Colorful groups of leaves at the bottom reflect light in ways underwater photographs will appreciate. The light play is a lot of fun as it comes trough the mangroves roots canopy.

The vegetation in the stream is thick. The water is sweet and for non experienced swimmers a floating device is a must as there is no place to get out in case of an emergency but returning to entrance. The stream twist a little so at certain point you are surrounded by jungle , as you continue swimming the cenote stream becomes very deep. Is in this area where manatees can be seen occasionally. The stream end in a rock plateau very flat . there is a place to jump out of the water and rest a while under the sun. there are a lot of white herons in this side of the stream. This cenote at tan Kah is one of the few  that had and underground waterway connecting to the ocean, the other one is at XpuHa Bay. This Than kah area is a very nice spot to spend some time. There is a very nice and reasonable priced restaurant there. The name is Casa Cenote. It is a very large and cool open palapa from where the beautiful turquoise Caribbean sea can be seen while enjoying a cool breeze non stop. After swimming in the cenote one can jump into the ocean crater like rock formation. Is only 12 feet deep and is full of colorful fish. There is no currents or undertow.

Casa cenote has an "exit" all to itself off of the main "highway" running north/south along the coast from Cancun to Tulum.  After parting ways with two dollars U.S. entrance fee we were greeted by cool, slightly brackish water. Immediately beneath the entrance area passages headed off towards the ocean. Swimming out into the sinkhole the basin led off into a wide swath of mangroves. Fining up into the trough several hundred feet we eventual came to the waters' entry point, a wide, flattened oval entrance partially obscured by massive chunks of breakdown and green aquatic growth gently bent in the direction of the flow.

Free diving down into the entrance you find yourself in a clean, scalloped avenue forty feet wide and ten feet high. Like all of my other experiences free diving in the area, once you got a hold on where it was and where it went the temptation was to hang around and keep trying to penetrate farther on with each successive dive. For the most part that's exactly what I did. And it was really, really fun. Obviously you have be careful, and not over-extend yourself.

Closer to the surface, along the basin's rim the mangroves send down armies of sharp, dark spires, infested with small silvery fish. Past the inland entrance you can dive down amidst these needles and make your way back into the brush, surfacing here and there until you find yourself floating in a dead-end, crystalline pond.

What was most interesting about this location was not the cenote but rather the cenotes' exit point.

A stones throw from the makeshift entrance to Casa the water that works it's way along the cenotes' belly resurges into the ocean. 

Wading out into tiny surf you can see the rise creating a billowing "slick" amidst the mellow chop of the Caribbean Sea. You can walk out to the edge of the marine spring and dive in as if it was a pool.

Beneath the surface a broad, shallow entrance fifty feet wide belches out the flow coming from Casa Cenote. What was a gentle, imperceptible current a couple of hundred feet inland is now a powerful and cold outflow, erupting forcefully into the salt water.

After a couple of tries, I figured out that the easiest way to get down into the entrance was to fin to the lip, turn upside down and then pull myself along the ceiling. Once past the mixing zone you could see clearly a wide, low passage heading off underneath the beach towards the cenote. Letting go of the ceiling, you were back in the current... regurgitated to the surface in short order.

The cenote known as Grand Cenote

A cave cenote type is the Aktun Chen. The access to the cenote is trough a natural tunnel in the rocks. Occasionally there are openings in the roof of the tunnel. As the sun light come trough over the trees growing out the tunnel. Looks nice and odd sensation . The there is a darker part of the tunnel until we reached a big quiet pond of underground water. Stalactites come down to the water mirror . lamps shed light in the place. The sensation is like to be inside a mother nature sanctuary , may be a natural sacred place. Swimming is not allowed in this cenote.