What he had found, unbeknownst to him at the time, was the ancient underground city of Derinkuyu. Derinkuyu was an entire city carved into the stone below Cappadocia, reaching some 60 meters down. It had 18 levels, and included residences, churches, food storage, wineries, and even a school. It was designed to house some 20,000 people as well as a number of livestock. It features vents to the surface and several discreet entrances like the tunnel found behind the wall. These hidden entrances suggest that the city was built as a precaution in order to shelter the population in times of war or natural disaster.