The underground city of Derinkuyu

The multi-level underground city of Derinkuyu lies in Turkey’s Cappadocia region. The complex, carved into tuff, includes rooms, narrow passages, ventilation shafts, a well, and a chapel; archaeological and museum descriptions also mention stables and heavy circular stone doors. It may have served as a refuge during periods of danger, but the popular estimate of “up to 20,000 people” is not a firmly established capacity.