It is considered unique for the quality and quantity of geological formations (speleothems) in its 17 miles length, 6 of which are open to the public.

In it are formations such as helictites (eccentric stalactites defying gravity) and curtains (draperies, or sheets of calcite, sometimes translucent, hanging from the ceiling).

The cave was accidentally discovered during drilling for mining, subsequently being exploited for the extraction of minerals.

On July 1, 2005 the Government of Cantabria opened it to the public and publicised it internationally, after development for tourism and protection rules prohibiting any further activity by the discovering club.

Artists like Bertín Osborne or Nando Agüeros have played inside the cave for hundreds of people in 2016.

The Sierra de Arnero runs parallel to the Cantabrian Sea, with a maximum altitude of 682 metres.

Here it remained unbroken 208 hours Speleo Club members Cantabria[2] highlight the cast, dyed red and white minerals in the area.

This is the list of minerals and fossils found in the cave, in alphabetical order: [citation needed]