A man knocked down a wall in his basement. He found an abandoned underground city that was once home to 20,000 people.

• Derinkuyu is a subterranean city in Turkey stretching 280 feet below the Earth's surface.
• The ancient city was used for centuries before it was abandoned in the 1920s.
• A local man rediscovered it in 1963 when he went looking for his lost chickens behind a wall.

Stretching 280 feet below the Earth's surface in Cappadocia, Turkey, is a web of tunnels and cave-like dwellings that once housed 20,000 people.

The ancient city, Derinkuyu, lay abandoned for decades until, in the 1960s, a local man noticed his chickens were disappearing through a gap in his basement that had opened up during renovations, the BBC reported. After knocking down a wall, he found a tunnel — and accidentally rediscovered the sprawling, subterranean city.

Now part of a UNESCO World Heritage site, Derinkuyu is open to visitors, although they can only explore eight of its 18 levels. Here's a closer look at the remarkable city and its history.