The town sits atop a labyrinth of tunnels, caves, and storerooms carved into the soft tufa, begun by the Etruscans and elaborated upon by the ancient Romans.
There is a small fee to access the underground labyrinth. 
mnli hypothesis: There is a small fee to access the underground labyrinth.  premise: The town sits atop a labyrinth of tunnels, caves, and storerooms carved into the soft tufa, begun by the Etruscans and elaborated upon by the ancient Romans.