Dos Ojos is a flooded cave system located north of Tulum, on the Caribbean coast of the Yucatán peninsula, in Quintana Roo, Mexico. It was first explored in 1987, and currently 51 mi (82 km) of the cave has been explored, with 28 sinkhole entrances being discovered.
Dos Ojos lies parallel and to the north of the Sac Actun cave system. Since its discovery, Dos Ojos has been one of the longest underwater cave systems in the world, and contains the deepest known cave passage in Quintana Roo, the Pit, which is 391 ft (119.1 m) deep. Some deep passages include the "Wakulla Room," the "Beyond Main Base passage," "Jill's room," and "The Next Generation passage." In August 2012 Dos Ojos was connected through a dry passage to Sistema Sac Actun. By May 2013, the total length of the combined system measured 193.22 mi (310.95 km).
Dos Ojos is an anchialine cave system with connections to marine water and tidal influence in the cenotes. The coastal discharge point(s) of this cave system have not yet been humanly explored through to the ocean, although large volumes of groundwater were demonstrated by dye tracing to flow towards Caleta Xel-Ha, a nearby coastal bedrock lagoon.
The name, which in Spanish means two eyes, is a reference to two neighboring cenotes that connect into a very large cavern zone shared between the two, thus appearing like 2 very large eyes. The original cave diving exploration began through these cenotes.
Water temperature is around 77 °F (25 °C) throughout the year, while the maximum depth near the Dos Ojos cenotes is approximately 33 ft (10 m). The water, due to being filtered by very pure limestone, is exceptionally clear.
There are several varieties of fish living in the cavern, the majority of which are well under 3.9 in (10 cm) long, and at least two types of freshwater shrimp.