Derinkuyu Underground City

Derinkuyu (ancient Elengubu) is the deepest known underground city in Cappadocia, Turkey, extending approximately 85 metres (280 ft) through 8 levels of soft volcanic tuff. Initially carved by the Phrygians in the 8th-7th centuries BC, it was greatly expanded during the Byzantine era with chapels, ventilation shafts, wine presses, stables, and storage rooms capable of sheltering up to 20,000 people with their livestock. Residents used it as refuge during the Arab-Byzantine Wars (780-1180 AD) and later Mongol invasions. Abandoned in 1923 when Turkey's Greek Christian population was relocated, the city was accidentally rediscovered in 1963 when a resident found a hidden room behind his wall.