Located in the Brenta Valley, in the little town of Valstagna, the sources of the Oliero are the most important hydric discharges of the Karst-massif of the Sette Comuni and the biggest Karst- springs of Europe. Four caves are open to the public at present: the Oliero river springs from the lower two caves while the visitors can find the upper ones, called "MURDERS' CAVE" and "SISTER' CAVES", walking on the path. Between the two main caves near the basin, which is completely encircled by the cool spring-water and immersed in the green of secular trees, there is the low and wide entrance of the "lords' cave" or "Parolini cave" which became the name from the discoverer who first explored it in 1822. The air temperature inside the cave is of 12 degrees, the water temperature is of about 9 degrees: these values keep steady all year round. The Oliero spring shelters in its waters a rare living fossil: the Proteus, an amphibian which lives only in the caves of the Slovenian and Triestinian Karst, brought by Parolini to verify its possibilities of adaptability. Lost sight of it, nobody knew anything about it till was sighted by some diving- speleologists in 1964, proof that Parolini succeeded in his attempt. Inside the cave of Parolini, that is possible to reach only by boat, everyone can see a great spectacle, as the dripstones' hall: a 14 metres high cascade of alabastrine stalactites which come down like waves, join together, overlap and finally part in a strange superimposition of form and colours. There are other internal halls which branch off from this one starting some tens metres above: these are the upper branches, exclusive apanage of the speleologists, which have been totally explored some years ago by the Grotte Giara Group of Valstagna.