Hidden in the sleepy Turkish town of Derinkuyu hides a vast underground city that once housed 20,000 people. Dating back thousands of years, the 18-storey subterranean marvel is 280 feet deep and has stables, granaries, kitchens, dwellings, a school, a church and more. 

Click or scroll through to explore the supersized labyrinth, find out why it was abandoned and how much we still don't know about this mysterious place...

The ancient underground metropolis was rediscovered in 1963 by a local man while he was renovating his basement. Local lore differs but in one version of the tale, the man inadvertently uncovered a small sinkhole after his chickens began mysteriously disappearing.

He dug his way through the hole to try and find them and to his absolute astonishment, the man found a large tunnel. He had discovered just one of the hundreds of entrances to the below-ground city that have since been identified, many more are located in private homes and some are situated in isolated areas hewn out of rock.

Derinkuyu is around 40 km from the area of Cappadocia in east-central Anatolia. Many aeons ago, violent volcanic eruptions blanketed the region  with colossal quantities of lava and ash, which set into a soft, porous rock called tuff. As well as being very susceptible to erosion, the soft rock is easy to carve and this, combined with a lack of moisture in the soil, makes it ideal for subterranean construction.

The ancient Hittite people are thought to have kicked off construction of what is now known as 'Derinkuyu Underground City' in 1200 BC, though some experts peg the start date at around 2000 BC and others as early as 3000 BC. There are around 200 subterranean cities in the region but Derinkuyu is said to be the largest and was first mentioned in a document in 370 BC. Following the find, archaeologists flocked to the site. Major excavations ensued and Derinkuyu Underground City opened to the public in 1969. 

The Hittites are purported to have begun construction of the underground metropolis, but are thought to be responsible for only the first few levels. Following the demise of the Hittite Empire in the 12th century BC, the Phrygians dominated the region until the seventh century BC. It was this civilisation that probably built the majority of the city.

Highly skilled, its craftsmen had the know-how to expertly carve the soft rock, which is fragile and prone to collapse. They hollowed out what's been likened to a human ant farm or rabbit warren with a myriad of tunnels, chambers and halls supported by strategically placed support pillars. No part of the city has ever collapsed, a testament to the brilliance of the Phrygian engineers.

Entering the city, you can't help but feel claustrophobic. Some tunnels are just five feet high and can barely fit one person at its narrowest point. The passageways, especially near the surface, were built to be as small as possible to slow enemy invaders.

The underground city has an area of 1.5 square miles but is spread out over a sprawling 172 square miles. It encompasses an estimated 18 levels and stretches 280 feet into the bowels of the earth. Just eight levels have been uncovered to date, meaning much of the metropolis is waiting to be discovered.

Over the centuries, the underground city was inhabited by Persians, Seljuks and other civilisations. However, it reached its full size and peak population of 20,000 around the seventh century AD, when Christian Byzantines used the subterranean metropolis for shelter amid multiple Islamic invasions. 

The city was carefully thought out, with livestock housed in stables on the first floor. Animals like sheep and goats are reluctant to go underground, so it made sense for them to live on the uppermost floor, where odours could also be minimised. Having the livestock on the upper level also provided an extra insulation boost for the storeys below.

Moreover, the human inhabitants of the city didn't have to worry about being suffocated by the toxic gases their animals produced.

The underground city was equipped with 50 main ventilation shafts and 15,000 smaller shafts that act as chimneys and circulate fresh air even to its lowest level. These shafts let in a modicum of light, too, and help regulate the temperature, which in most parts of the city is maintained at a brisk 55°F (13°C) all year round.

The cool ambience is a respite from the region's extreme seasons – summers are blisteringly hot, while winters are bitterly cold – and provides the optimum conditions for storing grain and other foodstuffs. Locals have revived the tradition of using the underground cities of the region as food storage hubs.

Though food storage was one of its key uses, the underground city mainly existed to provide a refuge in times of conflict. One of the ways the inhabitants protected the metropolis from invading forces was by shutting the rolling stone doors that are dotted around the tunnels.

Each weighing half a tonne, these sturdy circular doors have small holes cut in the middle, through which spears could be thrust to repel enemy troops.

Food was prepared in chambers decked out with traditional Anatolian floor furnaces located under ventilation shafts, which are remarkably effective at funnelling away smoke and smells.

The ovens are also known as tandoors and, like their Indian counterparts, were used to cook everything from meat to bread.

Olives were probably processed in industrial quantities in the kitchens.

On top of its food uses, olive oil provided the fuel for the underground city's lighting system, imbuing its tunnels, chambers and halls with a soft glow. The inhabitants would have been in the dark without it, making this one seriously important commodity.

A strong emphasis was clearly put on ensuring the inhabitants had adequate sustenance.

The frequently persecuted Byzantine Christians would have spent lengthy periods of time in the underground city. And the complex was used on and off by the local Cappadocian Greek and Armenian communities until the early 20th century as they sought refuge from Ottoman Empire oppression.

Water wasn't an issue in the city, which incorporates more than its fair share of wells. In fact, the modern Turkish name of Derinkuyu translates into English as “deep well”.

The underground city was known as Elengubu in ancient times, while the Cappadocian Greeks referred to it as Malakopi. Some sources suggest the name derives from the Latin Malacopia or Malagobia, which can mean “difficult subsistence”. After all, living in this dank, smothering place for long periods while enemy forces were marauding above can't have been pleasant. But it actually means "soft" in Greek and alludes to the rock the subterranean city is hewn from.

Located on the second level is one of the most distinctive structures in the underground city: the missionary school, which stands out with its barrel-vaulted ceiling.

Constructed during the Byzantine era, when disseminating the Christian faith was considered a duty, it features two study rooms to its side, as well as a baptistery.

A burial place is situated in the vicinity, as is a dramatic confessional booth.

A dark chamber with an entryway on either side, the priest would enter from one end, while the confessor would go in via the other.

The second floor is also home to the city's granaries. Bread was the staple of the civilisations that inhabited the underground metropolis over the centuries. Ensuring there was enough to go around for the upwards of 20,000 residents called for abundant space to store grain.

Grain would have been used to feed the animal inhabitants as well. If hostile forces were on the rampage, harvesting hay and other animal feed from the fields above would have been difficult if not impossible, so large supplies of grain were needed to keep the livestock alive.

Chamber after chamber on the second level was set aside to store the threshed wheat that sustained the denizens and animals of the underground city.

The subterranean metropolis seems to expand over an even wider area when you consider it's connected to an array of other underground cities in the region.

On the third level is a tunnel that links to the subterranean city of Kaymakli almost six miles away, as well as vertical staircases that descend to the lower floors.

Also, a passageway leads to the underground Hagia Maryeros Monastery, which is said to be the world's first mental asylum, and was considered a place of health and religion. 

The fourth level was reserved for living rooms, bedrooms and additional food stores. The floor where the inhabitants of the underground city spent much of their downtime would have been peppered with simple furniture and decorations, in contrast to how it looks these days.

Relaxing in this space would nonetheless have been a tall order with the constant worry raiding armies could infiltrate the sanctuary and cause carnage.

Ottoman persecution against the empire's Christian communities intensified in the 1910s, culminating in the Armenian Genocide and Genocide of Christian Greeks and Assyrian populations. An estimated 1.5 million Armenians were murdered, while up to 350,000 Greeks and 500,000 Assyrians are thought to have perished. Needless to say, the Christians of Cappadocia went underground to seek safety, moving their homes to the city's fourth floor.

Forcibly uprooted, the Cappadocian Greeks fled the region en masse in 1923. Their underground city, which had proved invaluable when it came to protecting the population from Ottoman aggression, was unceremoniously abandoned. Incredibly, the subterranean metropolis was completely forgotten about within Turkey, with memories of it fading over the decades.

The Cappadocian Greeks left little behind in the underground city, though they did of course leave their mark. The soft rock walls of the tunnels, chambers and halls are scrawled with what looks like graffiti in Greek and random doodles, likely scratched out when the inhabitants were holed up and bored to tears.

The archaeologists who explored the subterranean city following its rediscovery in 1963, exactly 40 years after its abandonment were amazed as they moved through the tunnels and realised the breathtaking scope of the underground metropolis. These tunnels must have been pretty scary back when they were illuminated with oil lamps, which provide relatively little light.

The lowest seventh and eighth levels are the most intriguing of all. They house a church in the form of a cross, though some scholars have argued the structure is clover-shaped, which would imply it was constructed by the ancient Hittites, who revered the symbol.

The lowest levels also feature a meeting hall punctuated by three large stone columns carved out of the rock. Rumour has it the hall doubled up as a dungeon at one time and graves are said to have been discovered in the complex.

Other spaces on the lowest floors defy explanation, with their use remaining a mystery.

A great deal of the underground city has yet to be revealed, but state-of-the-art imaging technologies, which are becoming ever more sophisticated, will likely uncover much if not the entirety of the metropolis in the coming years, with further excavations probable, too.

Derinkuyu Underground City has been a UNESCO World Heritage Site since 1985 as part of the Göreme National Park and the Rock Sites of Cappadocia designation.

World Heritage status commits the home nation to protect the designated monument, so it's likely the subterranean metropolis, which has endured for so many centuries, will be preserved for generations to come.