This area, near the mountain community of Vallo di Dano (310 m), is where the Italian horror director Dario Argento filmed “Il fantasma dell’opera” (“Phantom of the Opera”). The grotto is magnificent, surrounded by nature. It is of carsic origin and it started to form 35 million years ago, extending its perimeter for kilometres. As of today, though, you can only visit 2.5 km of it. You don’t walk through but float through it in a small boat. The entrance to the “Braccio delle meraviglie” (“corridor of wonders”) is unique and breathtaking. Numerous prehistoric remains have also been found inside the grotto.