The Vie Cave in Sorano and Sovana are quite evocative, pathways carved into the tuff hills by the Etruscans, a one-of-a-kind heritage whose true purpose remains a mystery even today. Maybe they were carved deep to reach the necropolis, in order to avoid the barrier of the mountains. Maybe they used them to hide from enemies, too. Anyway their function changed over the years, turning them into communication routes.
Make sure to visit the necropolis in Sovana, where you can find the via cava of San Sebastiano, with walls reaching as high as 20 meters, as well as the Cavone.