What Are Cenotes? — Mexico's Ancient Underwater World
Natural sinkholes filled with crystal-clear water, hiding millions of years of geological history beneath the Yucatan jungle.
Beneath the lush jungle floor of Mexico's Yucatan Peninsula lies one of the most extraordinary natural wonders on Earth: the cenotes. Pronounced seh-NO-tays, these natural sinkholes are windows into a vast underground world of crystal-clear rivers, ancient caverns, and geological formations that took millions of years to create. The Yucatan Peninsula is home to an estimated 6,000 to 10,000 cenotes, though some researchers believe the number could be even higher, with many still hidden beneath the jungle canopy, undiscovered and unexplored.
The word “cenote” comes from the Yucatec Maya word d'zonot (sometimes written ts'onot), meaning “sacred well” or “natural well.” For the ancient Maya, cenotes were far more than just water sources. They were considered portals to Xibalba — the underworld — and held deep spiritual significance. The Maya performed rituals at cenotes, made offerings of jade, gold, pottery, and in some cases, human sacrifices to appease the rain god Chaac. Cenotes were, quite literally, where the physical world met the spiritual one.
Today, cenotes are among the most sought-after natural attractions in Mexico. Divers, snorkelers, and travelers from around the world come to the Riviera Maya to swim in these pristine waters, explore underground caverns, and witness geological formations that predate human civilization by millions of years. But what exactly are cenotes? How did they form? And what makes them so unique?
How Cenotes Formed
Millions of years of geological processes created these underground wonders
The story of cenotes begins with the Yucatan Peninsula itself. Unlike most landmasses, the Yucatan has virtually no surface rivers or streams. The entire peninsula is made of porous limestone — the compressed remains of ancient coral reefs and marine organisms that accumulated on the sea floor over tens of millions of years. When the Yucatan eventually rose above sea level, this limestone bedrock became the foundation of the peninsula.
Rainwater, which is naturally slightly acidic due to dissolved carbon dioxide, slowly dissolves limestone as it seeps through the ground. Over millions of years, this process — known as karstification — carved out an incredibly complex network of underground caves, tunnels, and chambers beneath the Yucatan. The limestone acted like a giant sponge, with water filtering through and creating ever-larger passages.
During the Ice Ages, when sea levels dropped by as much as 100 meters, these caves were dry. This is when the spectacular formations you see in cenotes today were created. Stalactites grew downward from cave ceilings drop by drop, stalagmites rose from the floor, and columns formed where the two met. These formations took hundreds of thousands of years to develop, growing at rates as slow as one centimeter per century.
When the last Ice Age ended approximately 11,700 years ago, sea levels rose and freshwater flooded the cave systems. The formations that had grown in dry conditions were suddenly submerged, and the cenotes as we know them were born. Where the cave ceilings were thin enough, they eventually collapsed under the weight of the soil above, creating the openings — the cenotes — that connect the surface to the underground river systems below.
There is one more extraordinary element in this story: the Chicxulub asteroid impact. Approximately 65 million years ago, a massive asteroid struck the northern coast of the Yucatan Peninsula, creating the Chicxulub crater — the impact event that led to the extinction of the dinosaurs. The resulting fracture pattern in the limestone bedrock created a ring of weakness around the crater. Many of the Yucatan's cenotes are concentrated along this ring, forming a visible arc that traces the edge of the ancient impact crater. This geological coincidence means that when you dive a cenote, you are quite literally swimming in the aftermath of the event that ended the age of dinosaurs.
The Four Types of Cenotes
Cenotes are classified by their physical structure and how much of the original cave ceiling has collapsed
1. Open Cenotes (Cielo Abierto)
Open cenotes are completely exposed to the sky, resembling natural swimming pools or lakes surrounded by rock walls and jungle vegetation. The cave ceiling has fully collapsed, leaving a wide opening that allows direct sunlight to illuminate the water. These cenotes are often the most accessible and popular with swimmers and snorkelers. Examples include Cenote Azul and Cenote Cristalino near Playa del Carmen. Open cenotes can range from small pools to large lakes, and they typically feature sheer limestone walls, overhanging vegetation, and crystal-clear water that reflects the sky above.
2. Semi-Open Cenotes
Semi-open cenotes have a partial ceiling collapse, meaning they are partially covered by rock and partially open to the sky. This creates dramatic lighting effects as sunbeams penetrate through the openings and into the water below. Semi-open cenotes are among the most photogenic and popular with divers because of these stunning light shows. Cenotes like The Pit and Cenote Eden are excellent examples, where specific times of day produce columns of light that pierce through the water and illuminate the cavern floor in spectacular fashion.
3. Cavern Cenotes (Underground)
Cavern cenotes are primarily underground, with the cave ceiling mostly intact. You enter through a relatively small opening — often a narrow hole in the jungle floor or a set of stairs carved into the limestone — and descend into a vast underground chamber. These cenotes feature the most impressive stalactite and stalagmite formations because the ceiling has protected them from erosion and human disturbance. Dos Ojos, Tajma-Ha, and Dreamgate are famous cavern cenotes. Diving in these cenotes feels like entering another world — a cathedral-sized underground chamber adorned with ancient formations and illuminated only by your torch and the faint glow of daylight filtering through the entrance behind you.
4. Cave Cenotes (Fully Underground)
Cave cenotes are entirely underground with no direct opening to the surface above the water. Access requires entering through a connected cavern or through dry cave passages that lead to the water. These are the domain of trained cave divers who use specialized equipment, guideline reels, and redundant gas supplies to explore deep into the underground systems. The cave sections of systems like Ox Bel Ha and Sac Aktun extend for hundreds of kilometers into complete darkness. Cave diving in these systems is considered one of the most extreme forms of diving in the world and should only be attempted by properly trained and certified cave divers.
The Underground River Systems
The most extensive underwater cave systems on Earth
The cenotes of the Yucatan are not isolated pools — they are connected by an incredibly vast network of underground rivers that flow beneath the entire peninsula. These subterranean waterways represent the most extensive underwater cave systems ever discovered on Earth, and exploration teams continue to map new passages every year.
The three largest known systems are staggering in scale. Sistema Ox Bel Ha (meaning “Three Paths of Water” in Maya) is the longest underwater cave system in the world, with over 180 kilometers (112 miles) of surveyed passages. Sistema Sac Aktun (“White Cave”) follows closely with approximately 172 kilometers (107 miles), while Sistema Dos Ojos (“Two Eyes”) extends over 82 kilometers (51 miles). In 2018, explorers connected Sistema Sac Aktun with the Dos Ojos system, creating a single connected system of over 347 kilometers — though they are often still referenced separately.
These underground rivers carry freshwater from the interior of the peninsula to the Caribbean coast, where they discharge through submarine springs into the ocean. Along the coast, where freshwater meets saltwater, a fascinating phenomenon called a halocline occurs — a visible boundary layer where the two types of water meet but do not fully mix. Divers can swim through this layer and watch their vision blur as they pass between the freshwater above and the denser saltwater below. It is one of the most unusual sensations in all of diving.
The total length of mapped underwater cave passages in the Yucatan exceeds 1,600 kilometers (1,000 miles), and experts believe this represents only a fraction of what exists. New connections between systems are discovered regularly, and some researchers estimate the true extent of the underground network could be ten times what has been surveyed so far.
The Sacred Cenotes of the Maya
Portals to the underworld and the source of life
For the ancient Maya civilization, which flourished across the Yucatan Peninsula for over two thousand years, cenotes were far more than geological features. They were sacred places that served as the intersection between the earthly realm and the spiritual underworld. The Maya believed that cenotes were entrances to Xibalba — the realm of the dead, a vast underworld ruled by death gods and populated by the souls of the deceased.
The Maya word for cenote, d'zonot, reflects this sacred status. In a land with virtually no surface rivers, cenotes were the primary source of fresh water, making them essential for survival. Many major Mayan cities and settlements were deliberately built near cenotes, which served as the community's well. The Sacred Cenote at Chichen Itza, known as the Cenote Sagrado, is perhaps the most famous example. Archaeological excavations of this cenote have recovered jade jewelry, gold artifacts, pottery, obsidian tools, and the remains of human sacrifices — offerings made to Chaac, the rain god, in times of drought or to mark significant events.
The Mayan creation story, told in the Popol Vuh, features the Hero Twins who descend into Xibalba through a cenote to challenge the lords of the underworld. This myth underscored the cenote's role as a liminal space — a threshold between worlds. Ceremonies held at cenotes often involved the burning of copal incense, prayer, and the offering of precious objects thrown into the water as gifts to the gods below.
Today, many cenotes in the Yucatan are still considered sacred by the descendants of the Maya who live in the region. Local communities serve as custodians of cenotes on their ejido (communal land), and visitors are expected to show respect for the cultural and spiritual significance of these places. When you visit a cenote, you are stepping into a space that has been revered for millennia.
Extraordinary Archaeological Discoveries
Cenotes have preserved some of the most important archaeological finds in the Americas
The stable, oxygen-poor conditions in cenotes have made them extraordinary time capsules. The cool water and lack of currents means that organic material that would normally decompose in open environments can be preserved for thousands — even tens of thousands — of years. As a result, cenotes have yielded some of the most remarkable archaeological discoveries in the Western Hemisphere.
In the underwater caves connected to cenotes, researchers have discovered the skeletons of Ice Age megafauna that roamed the Yucatan during the Pleistocene epoch: giant ground sloths, saber-toothed cats, ancient camels, giant jaguars, and even mammoths. These animals fell into cenotes — likely while searching for water — and their remains were preserved in the cave systems for over 10,000 years.
Perhaps most remarkable are the human remains. In 2007, a team of cave divers discovered a nearly complete human skeleton in the Hoyo Negro cenote, deep within the Sac Aktun cave system. Named “Naia,” this 15-16 year old girl lived approximately 13,000 years ago — making her one of the oldest and most complete human skeletons ever found in the Americas. Her discovery provided crucial evidence about the early peopling of the continent and the genetic connections between the first Americans and modern Native populations.
Other cenote discoveries include Mayan pottery and ceremonial vessels, jade artifacts and jewelry, gold and copper objects, obsidian blades and tools, copal incense residue, and the remains of sacrificial victims dating back over a thousand years. Each discovery deepens our understanding of both the natural history of the Yucatan and the cultural practices of the civilizations that called it home.
Notable Discoveries in Cenotes
- Naia — 13,000-year-old human skeleton (Hoyo Negro)
- Giant ground sloth remains (multiple cenotes)
- Ancient camel skeletons from the Pleistocene
- Giant jaguar and mastodon fossils
- Mammoth bones preserved for 10,000+ years
- Mayan jade and gold offerings (Chichen Itza)
- Ceremonial pottery and incense burners
- Obsidian tools and weapons
The Cenote Timeline
From asteroid impact to modern exploration — the story of cenotes spans 65 million years
The Chicxulub Impact
An asteroid strikes the Yucatan Peninsula, creating a massive impact crater. The resulting ring of fractured limestone will eventually define the distribution of cenotes across the peninsula.
Dissolution Begins
Slightly acidic rainwater begins dissolving the porous limestone of the Yucatan, carving out underground channels and cavities that will become the cenote systems.
Caves Form Above Water
During glacial periods, sea levels drop dramatically, exposing the cave systems to air. Stalactites, stalagmites, and other speleothems grow over hundreds of thousands of years.
Sea Levels Rise
As glaciers melt at the end of the last Ice Age, sea levels rise and freshwater floods the cave systems. The formations that grew in air are now submerged, creating the underwater wonderland divers explore today.
The Maya & Cenotes
The Maya civilization builds sacred connections to cenotes, using them as water sources, ritual sites, and portals to the underworld (Xibalba). Cenotes become central to Mayan spiritual life.
Modern Exploration
Recreational cave and cavern diving begins in the Yucatan. Explorers map over 1,600 km of underwater passages, making it the most extensive underwater cave system on Earth.
Cenotes and Diving Today
How these ancient wonders became the world's most sought-after dive destination
Modern cenote diving began in the 1980s when a handful of pioneering cave divers first explored the underwater passages of the Yucatan. What they found astonished the diving world: crystal-clear freshwater with visibility exceeding 100 meters, massive caverns decorated with ancient stalactites and stalagmites, and an underground landscape that felt more like an alien planet than anywhere on Earth.
Today, cenote diving is divided into two categories: cavern diving and cave diving. Cavern diving is accessible to certified recreational divers (Open Water or above) and takes place within the cavern zone — the area of a cenote cave that is within sight of natural daylight and within a short swim of an exit. Cavern diving with a certified guide is a safe, awe-inspiring experience that does not require any specialized cave training.
Cave diving, on the other hand, ventures beyond the cavern zone into full overhead environments where natural light does not reach. This requires specialized training (typically a series of courses progressing from Cavern Diver to Intro to Cave to Full Cave Diver), redundant equipment, specific gas management planning, and the use of continuous guidelines. Cave diving is for experienced divers who have invested significant time and training into this discipline.
For most visitors, cenote cavern diving is the ideal way to experience these underground wonders. With a certified cavern guide, you will explore decorated passages, swim through columns of light, and experience visibility so clear that it feels like flying through air. Cenote snorkeling is another popular option — many cenotes have shallow areas where you can float on the surface and see the formations, fish, and geological features from above.
The water temperature in cenotes stays between 24 and 26 degrees Celsius (75-79 degrees Fahrenheit) year-round, and conditions are unaffected by weather, waves, or ocean currents. This makes cenote diving a year-round activity with consistently exceptional conditions — something no ocean dive site on Earth can match.
Come See Them for Yourself
No photograph or article can capture the feeling of diving into a cenote. The clarity of the water, the scale of the caverns, and the sense of stepping into deep time — it has to be experienced firsthand.