Underground City, Derinkuyu, Nevşehir Province, Turkey

The underground city at Derinkuyu could be closed from the inside with large stone doors. Each floor could be closed off separately.
The city could accommodate up to 20,000 people and had all the usual amenities found in other underground complexes across Cappadocia, such as wine and oil presses, stables, cellars, storage rooms, refectories, and chapels. Unique to the Derinkuyu complex and located on the second floor is a spacious room with a barrel vaulted ceiling. It has been reported that this room was used as a religious school and the rooms to the left were studies.
Between the third and fourth levels is a vertical staircase. This passageway leads to a cruciform church on the lowest (fifth) level.
The large 55 m ventilation shaft appears to have been used as a well. The shaft also provided water to both the villagers above and, if the outside world was not accessible, to those in hiding.