Geological site — Near Tychero, ~35km east of the city
Volcanic activity around 25 million years ago sent silica-rich solutions through the sediment here, replacing wood tissue molecule by molecule and locking entire tree trunks into stone. The centrepiece is a petrified oak roughly 20 metres long and 1.5 metres across, estimated at 35 million years old — one of the largest fossilised trunks found in Europe, still lying in the position it fell.
A small exhibit at the Tychero Tourist Centre, right by the town's lake, displays petrified leaves and smaller fossils from the wider find — cinnamon, fern, and an ancestral vine among them — alongside background on how the fossilisation happened.
It's a short, specific stop rather than a half-day plan, and pairs naturally with Lake Tychero next door.