One of the most famous underground cities in Cappadocia is Derinkuyu, built during the Byzantine era, when its inhabitants used it to protect themselves from Muslim Arabs during the Arab-Byzantine wars between 780 and 1180 CE. The multi-level city was composed of many passages and caves lying at around 60m (197ft) under the ground and was able to shelter around 20,000 people as well as their livestock and food. It’s certainly the deepest underground city in Cappadocia (and in all of Turkey). Derinkuyu was opened to visitors in 1969 – albeit, with only half of the city available for viewing.