We’ve all heard stories about the unbelievable things people find in their attics and basements. Most of the time, they discover old photos or family treasures, but no one thought that anyone would find something like this.

Back in 1963, a passageway was discovered under the house of a man in the Turkish city of Derinkuyu. At first, it didn’t seem like anything more than an ancient well. But the passage just kept going, and going, and going…

Tucked away in Turkey’s historical Cappadocia region lies the city of Derinkuyu.

Back in 1963, a passage was revealed beneath the home of one man living in the city.

Initially, he thought it might only be a crypt of some kind. But it turned out to be so much more.

The passage didn’t only lead to a single room. It led to a whole underground city.

The network of tunnels and chambers extended nearly 200 feet into the earth.

It’s believed to have held up to 20,000 people at one point, with all of their livestock and belongings.

Excavators found amenities like chapels, storage rooms, and even wine and oil presses.

There’s even a vaulted room that archaeologists believe used to be a school.

Not much is known about this underground city, but there are several theories regarding its origins.

One theory suggests that the city was built by the Phrygians between the 7th and 8th centuries.

But the presence of artifacts from several different peoples across time — from Zoroastrians to Christians — makes it extremely challenging to pin down the city’s exact origins.

It is agreed, however, that the city was probably used to hide great numbers of civilians during times of war.

A five-mile tunnel was found to connect Derinkuyu to another underground city, Kaymakli, though that one isn’t nearly as extensive.

Both cities are carved into rare geological formations, namely large deposits of soft volcanic rock that made excavation less difficult.

Parts of the city were sealed off with these huge stone doors, which were rolled into place to block the tunnels.

Passages like this one had “ladders” for people to make their way around.

The tunnels were made available to tourists in 1969, and can still be visited today.

It seems like it would be pretty simple to get lost down here.

Learn more about the underground city and its mysterious origins in this short documentary!

What an incredible piece of history. I can’t imagine finding something like this underneath my house!

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