Moraig is the name of an uderground river in southern Spain that, according to legend, was known by the Phoenicians 1000 B.C. However only its mouth, hidden among the sheer cliffs, was known because its origin has always been a mistery. In 1974 the speleologist Eloy Parra tried, for the first time, to discover the the origin of the river, also because the local population needed to find a source of drinking water. But the mission was unsuccessful.
In 1987 a group of German speleologists, with the help of international experts, began another search which lasted until 1990. This film records the efforts which led to the solution of the mystery.