While they were sheltering inside the cave they noticed that air was filtering through a hole in what was thought to be the rear wall above a huge stalagmite and that bats were flying back and forth as though there were another cave behind. In 1950 a team of researchers from Toirano knocked down the rear wall and discovered a 400 meter long series of corridors and caves full of beautiful formations, including a column shaped like the Tower of Pisa and a cluster of stalagmites christened the Organ because of the musical sounds they emitted when struck. Unfortunately, it wasn't until a good deal of damage had already been done that the researchers realized that the grotto contained traces of our own prehistoric ancestors and the cave bear. Besides paw prints and claw marks, there are also teeth and bones which constitute a veritable cemetery. Nowadays it is thought that the bears died during hibernation and many of the bones have revealed chronic diseases which certainly contributed to the process of extinction of these primordial animals.
Traces left by man include imprints of feet, knees, hands and fingers.
The footprints, which are unique, were made by broad feet with a fan-shaped spread of short toes, a wide front base, flat arch and a long heel, and are attributed to Neanderthal man. There are fragments of coal probably burnt by primitive man and balls of clay hurled against the walls in the Hall of Mysteries, the reason for which still remains, appunto, a mystery. The caves are open to the public and sometimes evening tours are organized, but check opening times and entrance fees.