Turkey's underground city of 20,000 people

More than 85m beneath the famous fairy chimneys of Cappadocia lies a massive subterranean city that was in near-constant use for thousands of years.

(This year, we published many inspiring and amazing stories that made us fall in love with the world – and this is one our favourites.)

Violent gusts whipped loose soil into the air as I hiked through Cappadocia's Love Valley. Pink- and yellow-hued hillsides coloured the rolling landscape scarred with deep red canyons, and chimneystack rock formations loomed in the distance. It was arid, hot, windy and devastatingly beautiful. Millennia ago, this volatile, volcanic environment naturally sculpted the spires surrounding me into their conical, mushroom-capped shapes, which now draw millions of visitors to hike or hot-air balloon in the central Turkish region.

But beneath Cappadocia's crumbling surface, a marvel of equally gargantuan proportions lay hidden away for centuries; a subterranean city that could conceal the whereabouts of up to 20,000 inhabitants for months at a time.

The ancient city of Elengubu, known today as Derinkuyu, burrows more than 85m below the Earth's surface, encompassing 18 levels of tunnels. The largest excavated underground city in the world, it was in near-constant use for thousands of years, changing hands from the Phrygians to the Persians to the Christians of the Byzantine Era. It 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. Not only do its cave-like rooms stretch on for hundreds of miles, but it's thought the more than 200 small, separate underground cities that have also been discovered in the region may be connected to these tunnels, creating a massive subterranean network.

According to my guide, Suleman, Derinkuyu 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 subterrestrial city of Derinkuyu.

Excavation began immediately, revealing a tangled network of underground dwellings, dry food storage, cattle stables, schools, wineries and even a chapel. It was an entire civilisation tucked safely underground. The cave city was soon spelunked by thousands of Türkiye's least claustrophobic tourists and, in 1985, the region was added to the Unesco World Heritage list.

The city's exact date of construction remains contested, but Anabasis, written by Xenophon of Athens circa 370 BCE, is the oldest written work that seems to reference Derinkuyu. In the book, he mentions Anatolian people, in or near the region of Cappadocia, living underground in excavated homes rather than the more popular cliffside cave-dwellings that are well known in the area.

According to Andrea De Giorgi, associate professor of classical studies at Florida State University, Cappadocia is uniquely suited to this kind of underground construction due to the lack of water in the soil and its malleable, easily mouldable rock. "The geomorphology of the region is conducive to the digging of underground spaces," he said, explaining that the local tuff rock would have been fairly easy to carve with simple tools like shovels and pickaxes. This same pyroclastic material was naturally forged into the fairy-tale chimneys and phallic spires jutting from the earth above ground.

But whom to credit with Derinkuyu's creation remains a partial mystery. The groundwork for the sprawling network of subterranean caves is often attributed to the Hittites, "who may have excavated the first few levels in the rock when they came under attack from the Phrygians around 1200 BCE", according to A Bertini, an expert in Mediterranean cave dwellings, in his essay on regional cave architecture. Adding weight to this hypothesis, Hittite artefacts were found inside Derinkuyu.

However, the bulk of the city was likely built by the Phrygians, highly skilled Iron-age architects who had the means to construct elaborate underground facilities. "The Phrygians were one of Anatolia's most prominent early empires," explained De Giorgi. "They developed across western Anatolia around the end of the first millennium BCE and had a bent for monumentalising rock formations and creating remarkable rock-cut facades. Though elusive, their kingdom spread to include most of western and central Anatolia, including the area of Derinkuyu."

Originally, Derinkuyu was likely used for the storage of goods, but its primary purpose was as a temporary haven from foreign invaders, with Cappadocia seeing a constant flux of dominant empires throughout the centuries. "The succession of empires and their impact on the landscapes of Anatolia explain the recourse to underground shelters like Derinkuyu," De Giorgi explained. "It was at the time of the [7th-Century] Islamic raids [on the predominantly Christian Byzantine Empire], however, that these dwellings were used to the fullest." While the Phrygians, Persians and Seljuks, among others, all inhabited the region and expanded upon the underground city in subsequent centuries, Derinkuyu's population swelled to its peak during the Byzantine Era, with nearly 20,000 residents living underground.

Today, you can experience the harrowing reality of life underground for just 60 Turkish lira (£2.80). As I descended into the musty, narrow tunnels, the walls blackened with soot from centuries of torch lighting, the unfamiliar sensation of claustrophobia began to set in. However, the ingenuity of the various empires that expanded upon Derinkuyu soon became apparent. Intentionally narrow, short hallways forced visitors to navigate the labyrinth of corridors and dwellings while stooped over and single file – obviously an inopportune position for intruders. Dimly lit by lamplight, half-ton circular boulders blocked doors between each of the 18 levels and were only moveable from the inside. Small, perfectly round holes in the centre of these hefty doors would have allowed residents to spear invaders while maintaining a secure perimeter.

"Life underground was probably very difficult," my guide Suleman added. "The residents relieved themselves in sealed clay jars, lived by torchlight and disposed of dead bodies in [designated] areas."

Each level of the city was carefully engineered for specific uses. Livestock was kept in stables nearest to the surface to reduce the smell and toxic gases produced by cattle, as well as provide a warm layer of living insulation for the cold months. The inner layers of the city contained dwellings, cellars, schools and meeting spaces. Identifiable by its unique barrel-vaulted ceilings, a traditional Byzantine missionary school, complete with adjacent rooms for study, is located on the second floor. According to De Giorgi, "the evidence for winemaking is grounded in the presence of cellars, vats for pressing and amphoras [tall, two-handled jars with a narrow neck]." These specialised rooms indicate that inhabitants of Derinkuyu were prepared to spend months beneath the surface.

But most impressive is a complex ventilation system and protected well that would have supplied the entire city with fresh air and clean water. In fact, it's thought that the early construction of Derinkuyu centred around these two essential elements. More than 50 ventilation shafts, which allowed for natural airflow between the city's many dwellings and hallways, were distributed throughout the city to avoid a potentially fatal attack on their air supply. The well was dug more than 55m deep and could be easily cut off from below by the city inhabitants.

While Derinkuyu's construction was indeed ingenious, it's not the only underground city in Cappadocia. At 445 sq km, it's merely the largest of the 200 and counting underground cities beneath the Anatolian Plains. More than 40 of these smaller cities are three or more levels deep beneath the surface. Many are connected to Derinkuyu via carefully dug tunnels, some stretching as long as 9km. All of them are equipped with emergency escape routes in case an immediate return to the surface was necessary. But Cappadocia's subterranean secrets have not yet all been excavated. In 2014, a new and potentially even larger underground city was unearthed beneath the Nevsehir region.

Derinkuyu's living story came to a close in 1923 when the Cappadocian Greeks evacuated. More than 2,000 years after the city's likely creation, Derinkuyu was abandoned for the last time. Its existence was all but forgotten to the modern world until some errant chickens brought the subterranean city back into the light.

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