In the maze of underground caves of the jungle of the state of Quintana Roo on the Yucatán Peninsula, Mexico, the longest known underground river flows. It is also called the most impressive Mexican attraction, which strikes with its marvelous geological formations. The  bends and turns of the water flow along the limestone caves extend to 215 km. It is included in the system of underground rivers called Sak Aktun. Its total length reaches several tens of thousands of kilometers.

The SakAktun water basin connects two complexes of underground cave systems. There is a distance of more than 181 km between them. According to the results of scientific research, the river appeared about 65 million years ago. Some people believe that in those distant times a large meteorite fell in the territory of the Mexican peninsula  which formed a huge crater (284 km), completely covered with numerous depressions and cracks. After some time, the funnel was filled with rainwater and as a result the formation of an unusual system of underground rivers appeared.