When you start a home improvement project, you often don’t know how it is going to turn out. It is hard to predict what you will find behind the walls of your home, which is why it is a good idea to set aside a little extra money to deal with any unexpected surprises.

In 1963, a man in Turkey began improving his home when he saw a crack in one of the walls. He chipped away at it to try to figure out where it was coming from, and eventually, he noticed that there was a narrow passageway behind the wall.

Upon further exploration, he found that the passage led to some rooms, and then more hallways, and even more rooms. By the time it was fully explored, the underground cave city stretched over 18 levels that went as deep as 85 meters (278 feet) below the ground.

Needless to say, historians and other experts were quick to come in and begin researching. They found that this city was built over the course of centuries and has been home to many people over the years.

At its peak, the complex could have housed as many as 20,000 people at a time.

Thanks to the design, carvings on the walls, artifacts, and other discoveries, researchers have identified meeting halls, stables, storage rooms, water wells, living spaces, wine cellars, weapon depots, burial tombs, and even prisons in the cave city.

Historians believe that this city was primarily used during times of persecution and war in order to house people safely. While there is dispute on which groups used it first, it is likely that the Hittites first carved the city about 3600 years ago.

After that, the Phrygians likely stayed there 2800 years ago, almost certainly expanding the ‘city’ according to their needs. Years later, the earliest Christians in the area used it to avoid Roman persecution, then centuries later, muslims used it during the Arab-Byzantine wars between 780 and 1180 CE.

As recently as the 14th century CE, Christians moved back in to escape the Mongolian invasions.

Today, the Derinkuyu underground city is a tourist attraction, and it has been recognized as a UNESCO World Heritage Site. Visitors can walk through the massive complex and learn about the incredible history that was only uncovered because of one man’s home improvement project.

If you thought that was interesting, you might like to read about 50 amazing finds on Google Earth.