Sac Actun Cave River System, Tulum Riviera Maya.
Sistema Sac Actun (from Spanish and Yucatec Maya meaning “White Cave System”) is an underwater cave system situated along the Cari Sac Actun Cave River System, Tulum Riviera bbean coast of the Yucatán Peninsula with passages to the Sac Actun Cave River System, Tulum Rivier north and west of the village of Tulum. Exploration started from Gran Cenote 5 kilometers (3.1 mi) west of Tulum. The whole of the explored cave system lies within the Municipality of Tulum (state of Quintana Roo).
In early 2007, the underwater cave Sistema Nohoch Nah Chich was connected into and subsumed into Sac Actun making it the longest surveyed underwater cave system in the world for some months. Sac Actun measures 228.3 kilometers (141.9 mi) (after connecting Sistema Aktun Hu with 34 kilometers -21 mi- in January 2011) and is second surpassed by Sistema Ox Bel Ha at 256.7 kilometers (159.5 mi). These two cave systems since early 2007 have been frequently exchanging the title as the longest underwater cave system in the world. Including connected dry caves and Sistema Dos Ojos makes Sistema Sac Actun with 317 kilometers (197 mi) the longest cave in Mexico and the second longest worldwide.
In March 2008, three members of the Proyecto Espeleológico de Tulum and Global Underwater Explorers dive team, Alex Alvarez, Franco Attolini, and Alberto Nava, explored a section of Sistema Aktun Hu known as the pit Hoyo Negro. At a depth of 57 meters (187 ft) the divers located the remains of a mastodon as well as at 43 meters (141 ft) a human skull that might be the oldest evidence of early man in this area to date.
Location Tulum Municipality, Quintana Roo, Mexico
Coordinates 20°14′47.6″N 87°27′50.8″W
Depth 101.2 meters (332 ft)
Length underwater: 228.354 kilometers (141.893 mi)
total: 316.601 kilometers (196.727 mi)
Discovery November 26, 1987
Entrances 169 Cenotes
Difficulty Advanced cave diving