As children, we all liked to imagine we were adventurers. Every forest path we trod was an ancient trade route; every shiny rock we picked up was a priceless gem; every hole we discovered was the mouth of a cavern that might lead all the way to the center of the earth.
When we got older, we realized our youthful Jules Verne-ian fantasies were almost always just that. Almost always.
In 1963, a man in the town of Derinkuyu in Turkey's Cappadocia region was doing some home renovations. When he knocked down a wall in his basement, he was alarmed to discover a secret room. Further excavations revealed a tunnel leading down into a subterranean city that had remained hidden for hundreds of years.
Unbeknownst to anyone, the modern above-ground city of Derinkuyu had all along been built atop the ancient underground city of Derinkuyu, a network of tunnels, chambers, and chapels large enough to house 20,000 people plus their livestock and supplies.
But who built this marvellous city? How did they do it? Why did they do it? And are there others like it? The answers may surprise you.
Perhaps most surprisingly, Derinkuyu is not by a long shot the only underground city in Cappadocia. There are at least 35 known, and likely dozens more waiting to be rediscovered. What makes Derinkuyu stand out is its truly remarkable size. This is an ant colony done up to human proportions, its five stories running to a depth of approximately 200 feet (80 metres). Altogether, the city is estimated to cover at least 1.7 square miles (4.5 square kilometres).
Derinkuyu's complexity also commands attention. Clean air was supplied from the surface to all levels by a system of 15,000 ventilation ducts, and there were wells to provide drinking water. The city was accessible from above via at least 600 hidden entrances. These could be blocked by large stones which were only movable from the inside, thus providing a foolproof way to keep out intruders.
Lest you think this is just the world's most impressive fallout shelter, Derinkuyu is far more sophisticated than that. Its builders furnished it with family suites, communal areas, what appears to be a study hall, a church, stables, and even rooms for pressing wine!
Dubious sources such as the History Channel's Ancient Aliens have bruited all manner of conspiracy theories about Derinkuyu and other subterranean lairs. Were they built by invaders from outer space? Is it true human technology couldn't have carved such an ambitious city out of stone?
There's no reason at all to think any of that. Cappadocia, the region of Turkey where underground cities abound, rests on a rocky plateau about 1 kilometre high. The entire region was buried in layers of ash from a volcanic explosion millions of years ago.
Over the eons, this ash petrified -- but it's softer than most other formations, making it relatively easy to carve and excavate. This was known to ancient peoples, such as the Hittites, who dug rooms into the volcanic rock in order to store food.
This is actually the more complicated question.
Some people think Derinkuyu was first excavated by the Hittites between the 15th and 12th centuries BC. Others think it was constructed later, by the Phrygians, an Indo-European group who lived in the Balkans, between the 8th and 7th centuries BC.
Whichever theory ultimately proves correct, Derinkuyu is as ancient as it is mysterious.
Not in dispute is the fact that the city was modified and expanded through the epochs, passed not merely from one generation to the next, but from one civilization to its successor. That's obvious enough from the greek inscriptions and the Christian chapels, and from the miles-long tunnels that were built by the Byzantines to connect Derinkuyu to other underground cities nearby.
Despite the complexity of Derinkuyu's design, and its many amenities, it's fairly obvious the city wasn't intended to serve a as a permanent place of residence. The secret entrances, the defence mechanisms, the built-in ability to lock the city from the inside alone -- all these point to Derinkuyu's intended purpose: a refuge.
And that makes sense. Turkey is one of the most strategically situated nations on earth. It straddles the Bosphorus Strait, connecting Europe with the Middle East and the Mediterranean with the Black Sea. Before the Ottomans took control of the region, it had been fought over fairly consistently for millennia. What better way to protect your people from raiders and invaders than to construct an underground sanctuary?
It also makes sense that people gradually forgot about these sanctuaries -- cities like Derinkuyu -- as society became more ordered and stable.
There are a number of tours available for those who want to visit Derinkuyu and Cappadocia's other underground cities.
That being said: visiting Derinkuyu may be inadvisable if you're claustrophobic, as the passages can be extremely narrow in places.