Derinkuyu is an ancient multi-level underground city

The underground city of Derinkuyu is an ancient multi-level underground city in the Derinkuyu district of Nevşehir province, Turkey, extending to a depth of about 279 feet.

It is large enough to shelter up to 20,000 people along with their livestock and food supplies. It is the largest excavated underground city in Turkey and one of several underground complexes found throughout Cappadocia.