These subterranean tunnels develop during an eruption of a crater: when the lava flows down the slope very slowly, it cools on the surface and forms a crust (like the skin that forms on a glass of hot milk); underneath, however, the hot lava continues to flow. When the eruption is over and no new lava comes from the underground, the resulting tunnel empties. What remains is an empty cave below the surface, which often is discovered much later or only by chance, e.g. the Grotta dei Tre Livelli on the south side of Etna near the Refugio Sapienza. This cave, which is over a kilometer long and spreads over three levels (hence the name), was created during the eruption of 1792 and was only found by chance almost 200 years later, during road works in the 1960s.
These caves scattered throughout the Etna area have represented for the population since ancient times, sometimes a precious shelter and sometimes an indispensable reserve of water or ice. But they also fueled the imagination of Greek writers who thus described this area with countless mythical and legendary characters.
A long, long time ago, the Cyclops Polyphemus, a one-eyed giant, lived in one of these caves with his sheep. Ulysses, the hero of the Trojan War, also passes Sicily and Mount Etna on his 10-year odyssey through the Mediterranean Sea back home to Greece. He comes to the cave of Polyphemus with his men and with wine and asks for hospitality. However, Polyphemus thinks they are thieves, locks them up in the cave and eats two of them for dinner.
Since they cannot roll away the stone that closes the cave on their own, they are trapped: they can neither kill Polyphemus nor escape. When Polyphemus also eats two men the next day, Ulysses devises the following ruse: he makes Polyphemus drunk with wine and when he sleeps, they blind his eye with a wooden stake. Polyphemus wakes up in pain, roars and lashes out, but cannot grasp Ulysses and his men because he sees nothing.
The next day, Polyphemus lets his sheep out of the cave and scans them all so that the Greeks do not get out of the cave. However, they throw themselves on sheepskins, Polyphemus takes them for sheep and they escape.
The Greeks flee to the beach and onto their boats; Ulysses, however, cannot help mocking Polyphemus from the ship. He ran to the beach in anger and throws huge boulders at the Greeks, but could not hit them. These rocks can still be seen today in the bay of Aci Trezza and are called Faraglioni di Aci Trezza.
If you do not want to believe that, you will get the following explanation (and learn how Etna was formed).
About 570,000 years ago, there was a large bay at the site of Etna, in which volcanic activity took place. The subsoil was soft, so the magma (that is underground lava) could erupt at any place.
Un tale vulcano viene anche chiamato vulcano a scudo. Nel tempo la baia si è riempita e gli strati di lava, roccia più dura del substrato preesistente, rendendo sempre più difficile l’eruzione del magma sottostante l’hanno portato a fuoriuscire in aree sempre più centrali, in corrispondenza della camera magmatica dell’Etna, dove la maggiore pressione riesce a fratturare più facilmente la crosta terreste.
Over time, the bay filled up; the spit out lava formed layers and thus made the cone of Mount Etna. Etna became a stratovolcano (strata = layers)..
In the time 570,000 years ago, when Etna was a shield volcano, also the Faraglioni of Aci Trezza were formed: the subsoil in the bay was still so soft that the lava could rise in this area, far from the center.
However, the lava did not always make it to the surface, when the pressure from below was not great enough.
Over time, the entire area has lifted, the softer material was washed away and the extremely hard lava remained.
The "faraglioni" were created.
The small archipelago, consisting of 4 larger rocks and some small ones, is also called Isole Ciclopi (Cyclops Islands) and is definitely worth a visit.