The 20-Million-Year-Old Petrified Forest on Lesbos
The name can be misleading: Lesvos's petrified forest is really only the remains of a prehistoric forest. On the other hand, those remains are 20 million years old, and the forest is just one of two found in the world.
The hike along the coast is worth it, and you'll be able to get up close to some of the old tree stumps. Their size is impressive; the trees must have been massive in their day! There is also a visitor's center onsite.