Two are the ancient caves dug into the side of the mountain on the north side at the end of '800 to build natural sudatorii, in a second time they were covered with masonry.
The visitors stayed inside the caves for no more than a few minutes, this caused a vigorous sweating forcing them to breathe the intense sulphurous fumes emitted.
Therefore they were considered excellent for the treatment of respiratory diseases, skin diseases and rheumatism. The natural sudatorii were well known, however, since the Classical Age and were one of the thermal attractions of Campi Flegrei.
