Derinkuyu underground complex, located in Turkish Cappadocia.
It was discovered accidentally when a man knocked down the wall of his basement. Upon arrival, the archaeologists revealed that the city was 18 stories deep and had everything necessary for underground life, including schools, chapels, and even stables.
Derinkuyu, the underground city of Turkey, is almost 3,000 years old, and once housed 20,000 people.
