The Lesvos Island UNESCO Global Geopark, one of the finest and rarest monuments of geological heritage worldwide and 2nd largest in all the world, is a founding member of the Geoparks Network that brings visitors to an ancient forest preserved by a massive volcanic eruption 20 million years ago. Known also as the Petrified Forest of Sigri, the Lesvos Island UNESCO Global Geopark features rare and impressive fossilized treetrunks, formed some 15 to 20 million years ago, due to intense volcanic activity that covered the trees by lava, ashes and other materials spewed into the atmosphere. Moreover, in the area of Lesvos Island UNESCO Global Geopark there are findings of the oldest known land mammal (Prodeinotherium bavaricum) 19 million years ago in Greece, impressive fossils of animals that lived on Lesvos 2 million years ago, numerous volcanic sites and thermal springs, faults and landscapes created from tectonism, caves and karstic structures, erosional forms and waterfalls as well as impressive coastal landforms all created by the intense volcanic activity some 21.5-16.2 million years ago.