Declared Natural Monument in 2002, it is one of the largest caves in Asturias. It consists of about 15 km of galleries of great speleological interest.
In our youth, almost all the boys of Fresnedo, my small village, made incursions in their galleries provided with helmets of carbide and lanterns.
Nowadays, only part of them can be visited. The rest of the cave is closed to preserve a colony of bats, an endangered species, that inhabit it.