Our Experience Sicily clients Eileen and Tony went deep into the earth’s surface with our expert Etna guides, when they entered a pitch black lava cave (Hence, the need for the hard hats and headlights.). Lava caves, also known as lava tubes, are formed during a volcanic eruption, when the outer part of lava flow cools faster than its center. Etna has more than 200 known lava caves. These natural phenomena can be visited, but don’t do so on your own. They are all different, are pitch black, and can be horizontal or vertical.