This giant cistern, arguably as magnificent as a subterranean cathedral, is one of Matera's great sights. Lying under the city's main square with arches carved out of the existing rock, it is mind-boggling in its scale and ingenuity, and was still supplying water to Materans within living memory. Book ahead for a 25-minute tour with the multilingual guides, who explain its conception and history (English-language tours generally leave at 10.30am, 12.30pm, 3.30pm and 5.30pm).