The Lesvos Island UNESCO Global Geopark, former Lesvos Petrified Forest Geopark, 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.
It features rare and impressive fossilised tree-trunks. The forest comprised enormous trees similar to those of the Sequoia family found today in North America – as well as pines, oaks, conifers and cinnamon trees. The fossilized trunks have retained fine details of their bark and their interior reveals a great variety of colors.
Not only ancient trees were fossilized but an entire ecosystem as well. Branches, fruits and leaves have also been preserved.
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 witnesses of the intense volcanic activity (21.5-16.2 million years ago), faults and landscapes created from tectonism, caves and karstic structures, erosional forms and waterfalls as well as impressive coastal landforms.
Source: https://en.unesco.org/global-geoparks/lesvos-island 
