Derinkuyu is located in the Nevsehir district of Turkey, 29 kilometres from Nevsehir. First opened in 1969, only 10% of the underground city is open to the public. It is thought that at one time up to 20,000 people lived in Derinkuyu’s 8 levels, extending 85 metres underground, with a possible 3 more levels yet to be excavated. Only 4 of these floors are open to the public, with a 55m circular descending ventilation shaft. This shaft was also used as a well, providing water to those inside and the villagers outside.
Each of the floors could be closed off separately, with circular doors which rolled and sealed from the inside. Derinkuyu has a unique feature in comparison to all other underground cities; it has a spacious barrel vaulted ceiling on the second floor. It is thought that this room was used as a religious school. Between the third and fourth levels is a vertical staircase leading to a cruciform church on the lowest level.
Derinkuyu was first built by the Phrygians between the 8th and 7th century BC. The Byzantines then enlarged the city between the 5th and 10th century AD. It was at this time that a large amount of the population was seeking religious refuge, especially Christians from the Roman Empire and during Arabs raids.