In 1963, a Turkish homeowner discovered the underground city of Derinkuyu while renovating his home. This extensive complex features 18 levels and was built around 1200 BC, initially by the Hittites. It was later expanded by the Phrygians and further developed by early Christians, adding chapels, stables, and facilities for producing wine and olive oil. Derinkuyu could house approximately 20,000 people, serving as a refuge throughout history during various invasions and conflicts.