Mexico is a country of caves and chasms, of new speleological explorations. For these men it is an essential part of life. They belong to a strange tribe, the cave seekers. For the Chol Indians, Shumula means the place where a lot of water comes out of the mountain. After 50 km, the Rio leaves the plain andenteres a deep gorge. At an altitude of 500 metres, the river leaves its course and disappears twice underground. The purpose of this expedition is to find the entrances and explore the underground course of this water.