Tufo is a volcanic rock that is what makes up the mountain on which the village of Orvieto sits. Under the town are about 1200 caves dug out by the villagers for survival over the centuries. This hypogeum started back with the Etruscans digging wells for survival and expanded to living quarters, pigeon holes for food, work places through medieval times, bomb shelter and hide out during WW!! and storage into modern times. A very interesting history here!