As soon as you enter you are dazzled by an intense blue and silvery reflections, which from the bottom stand out on the rock vault and walls. This is the reason that led the cave to be known as the “Blue Cathedral” and the writer David Foster Wallace to write about “a blue beyond the clearest blue imaginable”. It is such a unique and mystical experience that everyone in the world at least once in their life wants to live. It is thought that in the Roman age it was used as a maritime nymphaeum: for this reason, a tunnel at the bottom of the cave has suggested the existence of an underground passage on earth, with an Augusto-Tiberian villa in the upper part of Gradola, the so-called Villa of Gradelle. For many centuries the cave was feared by islanders, convinced that the place was infested with demons and witches, perhaps because frightened by the shadows and reflections of many statues still present inside and the blue color related to the curse and the devil.