Every day, millions of people walk above vast hollow spaces carved deep beneath their feet, unaware that below them stretch entire worlds designed to harbor human life. From ancient refuges that once sheltered tens of thousands from hostile armies to modern networks accommodating half a million daily commuters, these underground sanctuaries reveal humanity’s remarkable ability to dig deep when survival depends on it. Today, as urban populations swell and climate challenges intensify, these subterranean marvels offer both historical lessons and potential blueprints for future resilience.
The Ancient Fortress Beneath Turkey’s Fairy Chimneys
In 1963, a man renovating his basement in the Turkish town of Derinkuyu struck his sledgehammer against what he assumed was just another wall. Behind it lay a tunnel that led to more tunnels, eventually connecting a multitude of halls and chambers in a huge underground complex, abandoned by its inhabitants and undiscovered until that fateful swing. What he had stumbled upon was nothing short of extraordinary.
Derinkuyu Underground City was large enough to shelter as many as 20,000 people together with their livestock and food stores. The vast subterranean city extended up to 18 stories and 279 feet deep, housing what amounted to a small town’s worth of inhabitants. The city could accommodate up to 20,000 people and had amenities found in other underground complexes across Cappadocia, such as wine and oil presses, stables, cellars, storage rooms, refectories, and chapels.
The caves might have been built initially in the soft volcanic rock of the Cappadocia region by the Phrygians in the 8th-7th century BC, and when Greek replaced the Phrygian language in Roman times, inhabitants expanded their caverns to deep multiple-level structures. The city at Derinkuyu was fully formed in the Byzantine era, when it was heavily used as protection from Arab Muslims during the Arab–Byzantine wars. Underground cities, of which there were upwards of 200 in Cappadocia, were first and foremost always places of refuge, with the earliest archaeological record going back to at least 600 BCE.
Beijing’s Cold War Underground Metropolis
At the height of Soviet–Chinese tensions in 1969, Chinese Communist Party chairman Mao Zedong ordered the construction of Beijing’s Underground City. The complex was designed to withstand nuclear, biochemical and conventional attacks, protect Beijing’s population, and allow government officials to evacuate in the event of an attack, with the government claiming the tunnels could accommodate all of Beijing’s six million inhabitants.
The tunnels were built by more than 300,000 local citizens, including school students, on volunteer duties, with some portions dug without the help of any heavy machinery. In Beijing, some 300,000 people swung shovels digging an estimated 10,000 to 20,000 bomb shelters and some 30 km of tunnel linking them together, with every able-bodied men, even school children, taking part in the effort. The tunnels run beneath Beijing’s city center, covering an area of 85 square kilometres 8 to 18 metres under the surface.
The complex was equipped with facilities such as restaurants, clinics, schools, theaters, factories, a roller skating rink, grain and oil warehouses, and a mushroom cultivation farm, with almost 70 potential sites where water wells could easily be dug if needed. It was speculated that Beijing’s entire population at that time – 8 million – could disappear underneath and stay there for up to four months waiting for the air above to clear from a nuclear or chemical attack.
Montreal’s Climate-Controlled Underground Network
RÉSO, commonly referred to as the Underground City, is a series of interconnected office towers, hotels, shopping centres, residential and commercial complexes, convention halls, universities and performing arts venues that form the heart of Montreal’s central business district, with underground connections between buildings completely integrated with the city’s entirely underground rapid transit system.
Nearly 500,000 people use it per day, making it the largest underground complex in the world, stretching for 33 kilometers and covering 4 million square meters. According to official statistics, its corridors link up with 10 metro stations, 2 bus terminals, 1,200 offices, about 2,000 stores including 2 major department stores, approximately 1,600 housing units, 200 restaurants, 40 banks, movie theatres providing 40 screens and other entertainment venues, 7 major hotels, 4 universities, and 3 exhibition halls.
The network is particularly useful during Montreal’s long winters, during which time well over half a million people are estimated to use it every day. Urban planners designed it with the idea that this extensive indoor access area would reduce downtown traffic while also offering a way for pedestrians to circulate inside without having to go outdoors – especially during harsh winters when temperatures can drop below -20°C.
Engineering Marvels of Survival
These underground cities represent some of humanity’s most ingenious engineering solutions. Cappadocia’s unique landscape is characterized by soft volcanic tuff, formed by ancient eruptions, and this malleable rock was relatively easy to carve, yet strong enough to support the extensive network of tunnels and chambers without collapsing. The builders demonstrated remarkable sophistication in their designs.
The underground city at Derinkuyu could be closed from the inside with large rolling stone doors, and each floor could be closed off separately. The massive circular stone doors were capable of sealing off corridors from the inside, and these “rolling stones” could weigh several tons but were designed to be moved by a small number of people from within. Beijing’s complex featured elaborate ventilation systems with 2,300 shafts that could be sealed off to protect the tunnels’ inhabitants from poison gases.
The attention to detail in these underground environments is striking. Excavations at Derinkuyu have revealed evidence of domestic areas including kitchens with soot-stained ceilings, sleeping quarters, communal gathering spaces, stables for livestock, and storage rooms for grains and other foodstuffs, underscoring the self-sufficiency of the city during times of crisis.
Modern Underground Communities
Today, underground spaces serve vastly different purposes, yet they continue to house significant populations. In Beijing, anywhere between 100,000 to one million people live underground in old bomb shelters, dubbed the “rat tribe,” occupying cramped, musty, and windowless spaces located dozens of feet below the bustling streets of China’s capital city.
By the late 1980s, China’s government had started to liberalize and tensions with the Soviet Union had cooled, leading the Office of Civil Defense to lease these shelters to local landlords, who began leasing the spaces to desperate migrant workers and young people living dozens of feet underground as the only way to chase their dreams. A small unit can go for as little as $40 a month, and larger, dormitory-style rooms capable of housing as many as 10 people can be afforded for as little as $20 a month, with many residents believing underground dwelling is just a transitional phase until they gain financial means for a room with windows and sunlight.
Even in these challenging conditions, communities emerge. Organizations have been converting empty shelters into community centers, with spaces transformed into dining rooms, billiard rooms, karaoke rooms and calligraphy schools, providing residents living in Beijing’s concrete jungle an opportunity to mingle across societal classes that are otherwise somewhat rigid and imposing.
Why Underground Cities Matter for Global Security
The historical significance of underground cities extends far beyond their architectural achievements. These spaces have served as crucial refuges during some of history’s most turbulent periods. Derinkuyu was heavily used as protection from Arab Muslims during the Arab–Byzantine wars and continued to be used by Christian natives as protection from Mongolian incursions of Timur in the 14th century.
Even in the 20th century, the underground cities were still used by Cappadocian Greeks and Armenians to escape periodic persecutions, with a Cambridge linguist recording that when news came of recent massacres at Adana in 1909, “a great part of the population at Axo took refuge in these underground chambers, and for some nights did not venture to sleep above ground.” This pattern of refuge-seeking demonstrates the enduring value of underground spaces for civilian protection.
While Beijing’s complex has never been used for its intended purpose, it has never been fully abandoned either, with local authorities still performing water leakage checks and pest control in the tunnels on a regular basis. The persistence of these maintenance efforts suggests recognition of their potential future value.
Future Applications and Urban Planning
As urban populations continue to expand and climate challenges intensify, underground cities offer valuable lessons for future development. Montreal’s success with RÉSO demonstrates how underground networks can enhance urban functionality rather than merely serve as emergency shelters.
Today more than 33 kilometers of tunnels span Montreal’s network, covering over 12 square kilometers of the most densely populated area of the city, creating a vast indoor maze that has developed throughout the decades and incorporates much of the most important artistic and cultural venues. This integration of cultural, commercial, and transportation functions represents a model for sustainable urban design.
Recent discoveries continue to reveal the potential of underground spaces, with a newly discovered multilevel settlement in Cappadocia that may rival Derinkuyu’s size and features, appearing to have been a large, self-sustaining complex with air shafts and water channels where people retreated underground, blocked access tunnels with round stone doors, and sealed themselves in with livestock and supplies until threats passed.
Lessons for Modern Resilience
The underground cities that once sheltered millions offer profound insights into human adaptability and urban resilience. From the sophisticated ventilation systems of ancient Cappadocia to the comprehensive infrastructure of Cold War Beijing, these subterranean worlds demonstrate that with proper planning and engineering, underground spaces can support large populations for extended periods.
Today, as cities face increasing pressures from climate change, population growth, and security concerns, the principles behind these underground refuges remain remarkably relevant. The key lies not just in creating spaces below ground, but in designing them as integrated parts of urban ecosystems that enhance daily life while providing security when needed.
Whether serving as climate-controlled pedestrian networks like Montreal’s RÉSO or emergency shelters like those beneath Beijing and Cappadocia, underground cities prove that when surface conditions become challenging, humanity’s solution has often been to dig deeper. As we face an uncertain future, perhaps the question isn’t whether we’ll need such spaces again, but how quickly we can learn from those who came before us. What underground marvels might be waiting beneath your own feet?
Suhail Ahmed is a passionate digital professional and nature enthusiast with over 8 years of experience in content strategy, SEO, web development, and digital operations. Alongside his freelance journey, Suhail actively contributes to nature and wildlife platforms like Discover Wildlife, where he channels his curiosity for the planet into engaging, educational storytelling.
With a strong background in managing digital ecosystems — from ecommerce stores and WordPress websites to social media and automation — Suhail merges technical precision with creative insight. His content reflects a rare balance: SEO-friendly yet deeply human, data-informed yet emotionally resonant.
Driven by a love for discovery and storytelling, Suhail believes in using digital platforms to amplify causes that matter — especially those protecting Earth’s biodiversity and inspiring sustainable living. Whether he’s managing online projects or crafting wildlife content, his goal remains the same: to inform, inspire, and leave a positive digital footprint.
