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 Turkey’s Cappadocia region 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, though they can explore only eight of its 18 levels. Here’s a closer look at the remarkable city and its history.

Derinkuyu is an 18-level underground city in Cappadocia. It reaches 280 feet below the Earth’s surface at its deepest point.

Source: BBC

Cappadocia is a particularly good place for underground dwellings — its landscape is made of a volcanic-ash rock called tuff, which is pliable, dry, and easily carved.

Source: CNN, BBC

In 1963, a local man was remodeling his home and noticed his chickens were disappearing through a gap that had opened up. After he pulled back a wall, he found a tunnel that led to Derinkuyu.

Source: BBC

More than 600 entrances to the ancient city have since been found within people’s homes, the BBC reported.

Source: BBC

According to Turkey’s Department of Culture, it was built by the Phrygians in the eighth to seventh centuries BC. It was first referenced in a written text in 370 BC.

Source: Cappadocia Turkey, BBC

It was used for thousands of years — at first for storage and then as a place for people to hide from invasions and conflict.

Source: BBC

Its dwellers were able to survive underground for months at a time. At its peak, it was home to 20,000 people.

Source: CNN

But in the 1920s it was abandoned by the Cappadocian Greeks when they fled to Greece during the Greco-Turkish War.

Source: BBC

After the city was rediscovered in the 1960s, excavators found rooms for many purposes, including food storage, winemaking, oil pressing, and dining.

Source: Cappadocia Turkey

They also unearthed a chapel, pictured, and a religious school.

Source: Cappadocia Turkey

When the city was inhabited, livestock was kept on floors nearer the surface so their smells and gasses did not affect lower dwellings.

Source: BBC

A well provided clean water, and ventilation shafts allowed fresh air to circulate between the rooms and levels.

Source: BBC

Large stone doors on every floor were meant to stop intruders.

Source: Cappadocia Turkey,

A guide told the BBC reporter Geena Truman that life underground “was probably very difficult.” “The residents relieved themselves in sealed clay jars, lived by torchlight, and disposed of dead bodies in [designated] areas,” the guide said.