The rediscovery of an ancient underground city in Turkey a few years ago was an exciting find—the very kind of exciting find that the internet eats up.

The 5,000-year-old cave villa, found in the city of Nev?ehir, is fairly huge, with approximately 3.5 miles of tunnels, and dozens of rooms making up churches, tombs, and other safe spaces.

In comments to National Geographic, Nev?ehir Mayor Hasan Ünver noted that there was a bit of a paper trail that went back hundreds of years, but not one that implied that there was an entire city in the area.

"We found documents stating that there were close to 30 major water tunnels in this region," Ünver said.

It's not the first ancient underground city found in Turkey's Cappadocia region—people have been finding them since the 60s—but it's the largest, by far.

These days, urban dwellers think nothing of traveling under the surface as part of their average day. We'll dive into the metro or subway system without thinking anything about it.

But would you spend your entire day there, without walking outside? That sounds like an odd argument to make, but there was a period in which underground cities were seen as a bold, exciting solution to the problems that troubled the metropolis in the 1960s.

It was the revival of a concept that goes back thousands of years. Why didn't it stick?

A cave hotel is seen at sunset in the town of Goreme on April 17, 2016 in Nevsehir, Turkey.

Five things ancient underground cities have in common with modern ones

They're handy shelters from outside dangers: Modern underground cities are great ways to avoid being stuck in the severe cold or in the rain during a bout of severe weather. Ancient underground cities, like those in the Cappadocia region of Turkey, also served as a way to avoid outside dangers—but in their case, the outside dangers involved religious persecution, as the region was home to some early Christians.

They have areas to display artwork: The ancient catacombs of Rome have become noteworthy for their examples of early Christian art, but not to be outdone, Virginia's Crystal City, outside of the Washington, DC area, has become a hub of underground art.

They have consistent temperatures: One of the biggest benefits of an underground city in the modern day is that you probably won't be shocked by the temperature. It'll probably stay at a happy medium between hot and cold. Likewise, the caves in Turkey's Cappadocia region are known for keeping a consistently cool temperature—55° F, slightly nippier than your standard underground setting but perfect for storing fruit, as it turns out.

They're seen as potential economic drivers: For hundreds of years, Poland's Wieliczka Salt Mine represented the potential that an underground locale could have on an economy. The mine, which dates back to the 13th century, became incredibly important from a financial perspective due to salt's growing necessity in food. (It was still dishing out salt until 2007, shockingly.) And it became one of the world's first major underground tourist attractions, with chapels, dining halls, hotels, and other attractions making way after much of the salt was cleared. Ultimately, when an underground city is created today, this kind of economic success is the goal of the whole operation.

You can book a room in one: Most planned underground cities are associated with hotels, due to the fact that such hotels are common near downtowns. Since the discovery of the ancient caves in Turkey's Cappadocia region 50 years ago, parts of the caves have been converted to hotels as well. (Prices aren't bad, either; you can get a high-end room at the Cappadocia Cave Suites hotel for $150 a night.)