Derinkuyu is a quite recently rediscovered ancient underground city located near the modern town of Derinkuyu in Cappadocia. The city has 18 separate levels and extends to a depth of approximately 85 metres (280 ft), large enough to have sheltered as many as 20,000 people together with their livestock and food stores for months at a time.

Included with this extraordinary complex: wine and oil presses, stables, cellars, storage rooms, refectories and chapels. Located on the second floor is a spacious room with a barrel-vaulted ceiling. It has been suggested that this room was used as a religious school and the rooms to the left were studies. It is the largest excavated underground city in Turkey and is one of several underground complexes found throughout Cappadocia.

The city was built by the Phrygians, an ancient Anatolian people, around the 8th to 7th centuries BCE. However, it was significantly expanded and improved upon by later civilizations, including the Byzantines and early Christians, who used it as a refuge during times of war and persecution.

Originally, Derinkuyu was likely used for the storage of goods, but its primary purpose was to serve as a temporary haven from foreign invaders.

The city was ingeniously designed to withstand sieges and attacks, with massive half-tonne stone doors that could be rolled into place to block off passages. Each floor could be closed off separately.

The most impressive thing about Derinkuyu is its complex ventilation system (more than 50 shafts reaching the surface) and a protected well that would have supplied the entire city with clean water. The well was dug more than 55m deep. Incredibly, the city is also connected with another underground city, Kaymakli, via 8 to 9 kilometres (about 5 miles) of tunnels.

Derinkuyu’s underground city was finally abandoned in the 1920s by the Cappadocian Greeks when they faced defeat during the Greco-Turkish war and fled abruptly en masse to Greece. It was only "rediscovered" in 1963 by an anonymous local who kept losing his chickens. While he was renovating his home, the poultry would disappear into a small crevasse created during the remodel, never to be seen again. Upon closer investigation and some digging, the Turk unearthed a dark passageway. It was the first of more than 600 entrances found within private homes leading to the underground city of Derinkuyu.

Today, Derinkuyu is a popular tourist attraction, offering visitors a glimpse into the remarkable underground architecture and the ingenuity of ancient civilizations. If you’re interested in tagging along with Turkish YouTuber Ruhi Tenet in this video taken in the tunnels.
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References

wikipedia.org/wiki/Derinkuyu_underground_city
bbc.com/travel/article/20220810-derinkuyu-turkeys-underground-city-of-20000-people
atlasobscura.com/articles/derinkuyu-turkey-underground-city-strange-maps

Images

1. Derinkuyu Underground City. Credit: reddit r/interestingasfuck
2. Heritage version of Swiss based Oppidum's "luxury underground bunker"
3. Map of Turkey showing location of Derinkuyu. Credit: Google Maps.
4. Above ground modern day Derinkuyu. Credit: Getty Images.
5 & 6. Derinkuyu. Photo credit: Nevit Dilmen.
7. Ventilation shafts at Derinkuyu. Photo credit: Nevit Dilmen.
8. Video: "Inside the Underground City once Housed 20,000 People: Derinkuyu", Discover With Ruhi Cenet, 2022