Sac Actun is a flooded cave system under the jungle north and west of Tulum, with about 378 km of surveyed underwater passages. Gran Cenote is its best-known entrance, and Dos Ojos joined it in 2018. Visitors see it on a guided snorkel tour at the Sac Actun cenote site near Dos Ojos, or by swimming at Gran Cenote.
Sac Actun (“white cave”) is a flooded cave system under the jungle north and west of Tulum. Divers have surveyed about 378.6 km of underwater passages, 386.1 km counting the dry caves, with a deepest point of 119.2 m (January 2023 survey). You can see it two ways without cave training: swim at Gran Cenote, the entrance where exploration began, or take the guided snorkel tour at the Sac Actun cenote site near Dos Ojos, about 25 km north of town.
Checked October 2026:
| Underwater length | 378.56 km (Quintana Roo Speleological Survey list, 10 January 2023) |
| Including dry caves | 386.12 km |
| Deepest point | 119.2 m |
| Where exploration began | Gran Cenote, 5 km west of Tulum |
| 2018 connection | Sac Actun (263 km) + Dos Ojos (84 km) = 347 km |
| Longer system nearby | Ox Bel Ha, 541.7 km (CINDAQ, February 2026) |
In January 2018 divers with the Gran Acuífero Maya (Great Maya Aquifer) project, led by Robert Schmittner, found the link between Sistema Sac Actun, then 263 km, and Sistema Dos Ojos, then 84 km. The joined system measured 347 km and was reported worldwide as the longest underwater cave known. By caving convention the longer system keeps its name, so Dos Ojos became part of Sac Actun.
That record did not last. Sistema Ox Bel Ha, south-west of Tulum, has since been surveyed further: 541.7 km by February 2026, according to the annual report of CINDAQ, a cave research group. So Sac Actun is now one of the two longest underwater cave systems known, and both are near Tulum. Many travel sites, and the title of the tour on this page, still use the 2018 superlative. Mammoth Cave in Kentucky remains the longest cave of any kind.
The site sold as “Sac Actun” is not Gran Cenote. It is a separate cenote north of Tulum near the Dos Ojos park, run by an operator called Cenotes Sac Actun, whose area also includes the Pet Cemetery cenote.
Pet Cemetery is named, according to guides, for animal skeletons in the cave; we found no primary source for that. A dive operator’s fee list said it was closed to divers, with snorkelling still possible. That list is no longer online, so the status is not confirmed for 2026.
The GetYourGuide pick on this page is a private tour that visits Cenotes Sac Actun and Cenote Xunaan Ha, with pickup from Tulum, Playa del Carmen, Puerto Morelos or Puerto Aventuras.
Gran Cenote is 5 km from town on the Cobá road and is where exploration of Sac Actun began. You can swim and snorkel the cavern section that links its two pools on a normal ticket, reported at about 500 MXN in 2026 guides. It is the simplest way to swim in Sac Actun water.
Dos Ojos, now part of the same system, has a larger cavern and guided dives.
In 2007 cave divers Alejandro Álvarez, Alberto Nava and Franco Attolini found the way into Hoyo Negro (“black hole”), a bell-shaped flooded pit. At the bottom lay the skeleton of a teenage girl, about 15 or 16 years old, alongside the bones of Ice Age animals. She lived 12,000 to 13,000 years ago and is known as Naia. The project was directed by Pilar Luna Erreguerena of INAH, and the results were published in Science in 2014. Her mitochondrial DNA links her to modern Native Americans. The researchers describe her as the oldest, most complete and genetically intact human skeleton in the New World.
Sources disagree on which system Hoyo Negro belongs to: one places it in Sac Actun, another in a neighbouring system called Aktun Hu. Either way it lies in the flooded cave networks north of Tulum, and only technical cave divers can reach it. It is not open to visitors. The Maya cenotes guide has more on what has been found in the caves.
In June 2026 the newspaper Por Esto reported that a Tulum ring road was being built through jungle near Sac Actun and Hoyo Negro. An activist quoted in the article said Profepa, the federal environmental agency, had halted the works the year before for illegal clearing and that they had restarted. The article gave no documents, so treat these as claims.
Cavern dives at Gran Cenote and Dos Ojos need Open Water certification and a guide, and stay where daylight is visible. Everything beyond is cave diving and needs cave training. The cenote diving guide explains the difference.
The Sac Actun tour site is close to Dos Ojos and Cenotes Casa Tortuga. Gran Cenote is back near town. The Tulum cenote map shows both ends of the system, and the getting around Tulum guide covers the drive. For a base, see the where to stay in Tulum guide. Every cenote is on the Tulum cenote guide homepage.
5 hours
A private car tour to two very different cenotes, Xunaan Ha and Sac Actun, one a cave and one open to the sky, with a regional meal before the drive back.
Pickup: Tulum, Playa del Carmen, Puerto Morelos or Puerto Aventuras
from$189
Check availability4 hours
A morning run from central Tulum to Gran Cenote, the jump platforms at Cenote Zemway and the mangrove edge of Casa Cenote, with snorkel gear, towels and transport between stops.
No pickup: meet on site
from$135
Check availability1 day
A self-guided admission ticket to both linked basins of Dos Ojos with a life jacket, for people who want to swim the famous cavern at their own pace.
No pickup: meet on site
from$43
Check availability5.5 hours
Two guided cavern dives on different lines at Dos Ojos for Open Water divers, with lights and 5 mm wetsuits supplied and groups of four at most.
No pickup: meet on site
from$199
Check availabilityPrices and ratings were taken from GetYourGuide and can change. Booking through these links supports this site at no extra cost to you.
It was, from January 2018, when divers connected it to Sistema Dos Ojos and made a 347 km system. It is not now. Sistema Ox Bel Ha, south of Tulum, had 541.7 km surveyed by February 2026, according to the cave research group CINDAQ. Sac Actun, at about 378 km underwater, is one of the two longest known, both near Tulum.
Not exactly. Gran Cenote is one of the entrances to Sistema Sac Actun, and exploration of the system began there. But the place sold as the Sac Actun cenote tour is a different site, north of Tulum near the Dos Ojos park, run by an operator called Cenotes Sac Actun. Both let you see part of the same system.
The operator's website lists USD 40 per person, but the site looks old and the price is undated. A visitor review reports 650 MXN for a one-hour group tour including wetsuit, mask and life jacket, paid by cash or card. Another 2026 guide converts the price to about 290 MXN. Check directly before you go.
In 2007 cave divers found the skeleton of a teenage girl, later named Naia, in a flooded pit called Hoyo Negro, alongside Ice Age animals. She lived 12,000 to 13,000 years ago. Researchers call her the oldest, most complete and genetically intact human skeleton in the New World. Sources disagree on which cave system Hoyo Negro belongs to.
Certified divers can dive parts of the system with a guide. Cavern dives at entrances such as Gran Cenote and Dos Ojos need Open Water certification and stay within daylight. Going further needs cave training. A dive operator's list said the Pet Cemetery cenote at the Sac Actun site was closed to divers; that is not confirmed for 2026.
Gran Cenote is a semi-open cenote 5 km west of Tulum on the road to Cobá: two clear pools joined by a cavern, with wooden walkways and resident turtles.
Cenote Dos Ojos, the two eyes cenote, is a pair of cenotes joined by a large cavern in Parque Dos Ojos, about 22 km north of Tulum off Highway 307.
Cenotes Casa Tortuga is a cenote park on Highway 307 at km 239, about 14 km north of Tulum, where a guide leads you through open and cave cenotes.