When renovating a house, people generally will learn a few more things about their humble abode that they didn’t know before. But usually that doesn’t involve discovering a city that’s been lost for centuries.

In 1963, a man living in Nevsehir, Turkey knocked down a wall in his basement while doing some work on his home and found a tunnel he never knew about. The tunnel led to the ruins of the underground city of Derinkuyu.

The city was originally founded sometime during either the 7th or 8th century B.C. During the Arab-Byzantine wars between 780 and 1180 A.D., many Christians used the underground city as protection from the violence, and then was used for the same purpose during the Mongol invasions of the 14th century.

Derinkuyu was still populated until the early 20th century when the Ottoman Empire fell. It was completely untouched until this guy found it behind his basement wall in 1963.

Below is an illustration of how Derinkuyu was used. At it’s height, the underground city held up to 20,000 people.

This rock was used to block the entrance into the city. The hole is for a large rod to be put into it to move and allow people to get in.

The city was entirely functional with churches, cafeterias and schools.

Derinkuyu was opened up for tourist visits in 1969. And to think it could’ve gone unknown for years if one guy didn’t hit his sledgehammer a little too hard into his wall.