Dos Ojos Cenote

How did divers map 82 kilometers of passages at Dos Ojos?

Dos Ojos, two eyes, is a pair of neighboring cenotes that open onto the same large cavern zone, like two eyes onto the underground world. Diving exploration started here in November 1987 and is still going: 82 kilometers of surveyed passages, 28 entrances, and a maximum depth of 119 meters reached at The Pit, discovered in 1996 from the main entrance, 1,500 meters away. Long ranked among the three longest underwater cave systems in the world, Dos Ojos was connected to Sistema Sac Actun by a dry passage in 2012, then underwater in January 2018, and is now part of it: together they form the longest known underwater cave network. The site was a set for the IMAX film Journey Into Amazing Caves in 2002, for the Planet Earth series in 2006, and for scenes of the film The Cave in 2005. In November 2010, freediver Carlos Coste swam 150 meters there on a single breath, a world record.

Why does the cavern briefing at Dos Ojos matter?

It all starts in front of the park's signboards, before you head down the stairs. The guide explains the line: the main one is gold, the secondary ones white and thinner, and when you see a white one, you have left the route. You stay within arm's reach of the line and never lose sight of it. Losing the line is the leading cause of fatal accidents in cave diving, entanglement the second, and strap fins or dangling gauges get caught in it. Everyone carries two lights, with the main one on the whole time, because the guide counts lights, not divers. Air is managed by the rule of thirds. You carry half the weight you would use in the sea, so you can swim flat, fins up above head level, with a frog kick, without touching the formations or stirring up the silt. Four divers per guide, no more. And if anyone pushes you beyond the cavern zone without a cave certification, say no.

Cavern or cave diving: what can you do at Dos Ojos?

Cavern diving is recreational diving: you stay in the zone where daylight is visible, with no obstacle between you and the surface, less than 60 meters from the exit, 40 for some agencies, and shallower than 20 meters, 30 for others, with standard gear. Beyond that it is cave diving, which is technical: a cave diver certification, a dedicated configuration, sometimes trimix and decompression stops. At Dos Ojos, Barbie and Bat Cave are cavern routes; the 82 kilometers that open up behind them are reserved for trained and equipped cave divers. The Pit, three kilometers away, is a case of its own: an open shaft where you descend to 30 or 40 meters in full light, and it requires Advanced.