Extending for a total of 3,200 metres, this underground cave is surrounded by salt, wells and tunnels connected to each other thanks to the action of the rainwater: over the millennia, it has infiltrated a system of carbonate rocks, digging - through the ages - different levels of underground cavities. Only the lower section, 530 metres long, is without difficulty and ends with the Pissai waterfall, more than 40 metres high.

The first written testimonies of the Grotto, recorded by scholars and mountaineers, date back to 1600. In addition to being an important habitat for the community, the Rio Martino cave also has a high ecological value because it hosts a rare and extremely specialized fauna: numerous invertebrates and at least 10 different species of Bats, including the Geoffroy’s bat, lesser mouse-eared bat, Daubenton’s bat and barbastelle bat, especially during hibernation.

The delicate underground ecosystem and the populations of wintering bats are very sensitive to the effects of human presence. For this reason, the cave can only be visited in the summer months, while access is forbidden from 1 November to 31 March (a period that can be extended depending the climatic conditions). The cave can only be visited accompanied by a guide.

Visitors must wear appropriate clothing as the temperature inside is about 5° C and the humidity is around 100%. The cave is in absolute darkness and it takes about two hours to walk the lower section, up to the Pissai Waterfall and back.