Derinkuyu Underground City is an ancient multi-level underground city located near the town of Derinkuyu in Turkey. It extends to a depth of approximately 85 meters and could shelter up to 20,000 people along with their livestock and food stores. The city features amenities like wine and oil presses, stables, cellars, storage rooms, refectories, and chapels. It also has a unique room with a barrel-vaulted ceiling that was possibly used as a religious school. The city dates back to the Byzantine era and was used as protection from various threats throughout history. Today, visitors can explore about half of the underground city, which was rediscovered in 1963.