Why Does This Ancient 20,000 person Underground City Exist? (Derinkuyu)

We explore the underground cities of Cappadocia, descending through tunnels, chambers, churches, wineries, ventilation shafts and defensive gates while learning about their history and engineering from a local guide. We discover that the cities could shelter 15,000 to 20,000 people, extend dozens of meters underground and remain largely unexcavated. We then venture deeper into the darkness, reflect on the people who once sought refuge there, and spend the night underground before emerging the next morning.