Sistema Sac Actun

Grand Cenote: The starting point of the research

Sac Actun ( Mayathan Aktun sak, white cave; Sistema Sac Actun officially ) is an underground river system in the Yucatan Peninsula in Mexico. It is with 222.7 km while at the second- longest known underwater cave system. It is connected by 163 Cenotes with the surface; the greatest depth is located at The Blue Abyss 101.2 m.

In August 2012, a connection to the more northerly 82.4 km long Sistema Dos Ojos in the range of Nohoch Nah Chich was found over a dry passage. Inclusive of all above-water parts ( 5.8 km ), the total length of 311 km; Sac Actun thus / Dos Ojos is the world's second longest cave system.