Underground City, Turkey (Derinkuyu Yeraltı Şehri)

In 1963, a man in the town of Derinkuyu was renovating his home. He knocked through a basement wall and found a room on the other side. Behind it was a passage, and behind that, another. What he'd broken into was an entire city carved into the rock beneath his town. The rock under Cappadocia is tuff, compacted volcanic ash that is soft enough to carve by hand but strong enough to hold its shape. For thousands of years, people in this region dug into it. The first chambers at Derinkuyu may have been cut by the Phrygians as early as the 8th or 7th century BC. Over the centuries, later inhabitants kept digging, deeper and wider. The city reached its full form in the Byzantine era, and it grew significantly during the Arab–Byzantine wars, roughly 780 to 1180, when raiding armies swept across the plain. When danger came, whole communities went underground, bringing their animals and food with them. At its largest, Derinkuyu reached about 85 meters (280 feet) deep and could shelter as many as 20,000 people. It was built to be lived in under siege. There were stables near the surface, along with kitchens, storerooms, wine and oil presses, chapels, and a large barrel-vaulted room on the second level that may have been a school. A network of ventilation shafts carried fresh air down through every level, and one 55-meter shaft doubled as a well. Each level could be sealed from the inside with massive round stone doors that rolled across the passages. Derinkuyu wasn't alone. More than 200 underground settlements have been found in the region, and tunnels 8 to 9 km long are believed to connect Derinkuyu with the underground city at Kaymaklı. People kept using these shelters for centuries: during the Seljuk invasions, during Timur's campaigns in the 1300s, and into the early 20th century, when local Cappadocian Greeks and Armenians still sought refuge underground. That ended in 1923, when the population exchange between Greece and Turkey sent the region's Christian population to Greece. The underground city was left empty, and memory of it faded. Forty years later, one basement wall brought it back. Since then, more than 600 separate entrances have been found, some hidden beneath the houses of the modern town above. Derinkuyu opened to visitors in the 1960s and is part of the Göreme National Park and the Rock Sites of Cappadocia UNESCO World Heritage Site, inscribed in 1985. Much of the city has still never been opened to the public.