The largest underground city - Derinkuyu - consists of several levels reaching 80 meters deep into the ground and could have provided shelter for up to 20,000 people.
Construction of Derinkuyu began in ancient times, probably around the 8th century BC. The builders were most likely Phrygians. After them, the underground residential complex began to be deepened and enlarged by subsequent land inhabitants.
Kitchens, dining rooms, toilets, private quarters and a hall for congregations were built on subsequent levels. Byzantine Christians created numerous chapels and a church there and expanded the city, which eventually had several levels and reached 80 meters into the ground. Construction continued for more than a dozen centuries, until the 12th century. In addition, Derinkuyu was home to wine and oil factories, stables and warehouses for storing food, as well as a cemetery.
The underground city has a ventilation shaft measuring 55 meters, which was also used to supply water. A water pipeline running along it provided water to residents in times of danger, while during peacetime, it served villagers on the surface. In summer, the temperature inside the city stayed at 15 °C (59 °F), while in winter, the air temperature dropped to 7 °C (45 °F).
The city could be accessed through hidden and scattered entrances. In strategically important parts of the city, round stone doors weighing up to 500 kilograms blocked the way of enemies. These boulders could not be pushed back from the outside.
Derinkuyu was connected to other underground cities existing in Cappadocia by many kilometers of tunnels, where archaeologists have found artifacts dating from the 5th to 10th centuries AD.
