To talk about volcanoes and the Aeolian Islands is to speak of the same thing. The whole archipelago is built on a volcanic arc, caused by the movements of plates and the rock formations which began half a million years ago. This area, geologically still "young", extends to the north and west. It includes other underwater islands which have never emerged from the sea, while the volcanoes which shaped the landscape are largely extinct, although still evident in the underwater gas streams and hot thermal springs. The most famous of these are in San Calogero, used for more than 2,000 years, where, next to the Eighth Century building, there is a Tholos - an ancient Greek round structure of the Mycenaean age, where the waters ow and the air is saturated with beneficial vapours. The islands' active volcanoes are a 'must' for those who are passionate about earth sciences: Stromboli, which has long been a landmark for sailors who travelled these Aeolian routes between Sicily and the Italian coast, and is still considered the "Lighthouse of the Tyrrhenian Sea", whose intermittent lava streams ow like waterfalls down the "Sciara del Fuoco" or "Stream of Fire"; Vulcano, which has been deep in peaceful sleep since its last great eruption in 1888, can be heard snoring softly as you approach the area around the crater; Panarea, meanwhile, hides its active volcanic nature among the sea urchins and seagrasses that cover the seabed around the islets of Lisca Bianca, Bottaro and Dattilo, where emissions from the underwater craters create columns of bubbles of spectacular intensity.