The Grotte di Oliero are several caves which are the springs of the short fiume Oliero (Oliero river), a tributary of fiume Brenta (Brenta river). The most interesting is the Grotta Parolini, originally called Covolo dei Siori (Cave of the Lords), but renamed Grotta Parolini in honor of the first explorer Alberto Parolini. The trail on the left side of the river also leads to two dry caves, located on the slopes above the spring. The Covolo degli Assassini (Grotto of the Murderers) and the Covolo delle Sorelle (Grotto of the Sisters). Back at the river Oliero, it is possible to cross it on the old mill dam and follow the right shore of the river upstream to the other spring of the Oliero. This deep blue pot at the foot of a limestone cliff is called Cogol dei Veci. Wooden boat brings visitors continually across the lake and back to quay. So these caves unite a subterrean river, a boat cruise a short walk inside the cave with the main spaleotherms of a carstic cave. To return to the entrance, the visitors have the choice between four hikes to do. You can admire the most important exo- and endocarstic forms during a half-day trip from Bassano del Grappa or Trento. The prices are moderate and the team is very friendly and helpful. If you still have some time, you should book in advance a rafting trip with the Valbrenta-Team on the Brenta.