Derinkuyu Underground City

History suggests that the Hittites first built Derinkuyu Underground City approximately around the year 2000 BCE. The construction expanded during the Byzantine period and was used as protection from Arab attackers. The city is 85 meters deep and has more than 18 levels although only eight can be visited. It has been claimed that during some crises conditions 20,000 people and animals and food stocks could be settled in Derinkuyu.

 This latter place is a center of religious activities which had churches and a large cruciform chamber. Even the most remote areas of the city had efficient ventilation systems that supplied fresh air.