More than 1,200 artificial and natural caverns have been found in the pozzolana (a volcanic stone powdered to make cement mix) and tufa rock upon which Orvieto rests. Guided tours take in just two, 15m (45 ft.) below Santa Chiara convent, reached by a steep climb up and down 55 steps, along a narrow rock-hewn passage. The caverns have variously been used as Etruscan houses, water wells, ceramic ovens, pigeon coops, quarries, and cold storage (the temperature is a constant 14C/58F). Residents took shelter in them during World War II Allied bombings, but most unwisely—a direct hit would have annihilated the soft rock.
To look at Orvieto’s tufa foundations from the outside, take a hike along the rupe, a path that encircles the base of the cliff. A landmark along the way is the Necropoli Etrusca di Crocifisso del Tufo (Etruscan Necropolis), where tombs are laid in a street-like grid in subterranean caverns (3€; daily 8:30am–5:30pm). The tourist office can supply a map, Anello delle Rupe.