From colossal underground cities to scientific test sites and nuclear facilities there are many secret places that can be found deep underground. Underground structures are challenging to build. When we build down rather than building up, issues like soil science, structural stability, and waterproofing all become increasingly important. As experts in basements, crawl spaces, and foundations, we’re familiar with the unique challenges of underground construction. Yet around the world, there are amazing underground sites that are engineering marvels.
Here are the top 10 biggest underground structures in the world.
1. Derinkuyu
For most people, it’s normal to wake up with light streaming through their bedroom windows. However, in the Turkish city of Derinkuyu, its location of up to 85 meters below ground made this simple pleasure impossible for a staggering 20,000 people. Now, exactly who built this city is up for debate. Some scholars argue that the oldest part of the complex could have been dug out in about 2000 BC by the Hittites; others instead attribute the city to the Phrygians, who would have built it around 700 BC.
Still, others claim that local Christians built a city in the first centuries A.D. Yet, no matter who actually founded it, there are two things about Derinkuyu that are certain. First and foremost, the city was built underground to help people hide from enemy armies. After all, rolling stones were used to close the city from the inside, which would have insulated people against outside attack. The second is that very few final changes to the city were made by Christians between the 6th and 10th centuries A.D., after which the site was more or less left as is.
Once you begin to explore its depths, it soon becomes clear that Derinkuyu is a marvel of human engineering. It’s ventilated by a total of more than fifteen thousand shafts, most are about 10 centimeters wide and reach down into the first and second levels of the city, allowing for good ventilation all the way down to the eighth level. It’s within this well-ventilated area that people lived and slept, with cool facilities such as a wine press, domestic animal section, convent, and small church being present.
However, a total of 18 levels exist, with the lowest and least ventilated levels being mainly used for storage wells and, curiously enough, a dungeon. The creation of such a wonderful city was possible thanks to the area’s unique geography. You see, the rocky areas of the region consist of tuff, which is a substance that’s made primarily out of volcanic ash. Fortunately, tuff is very easy to dig due to the fact that, rather ironically, it’s not very tough.
And it’s this softness that allows such an extensive tunnel system to be dug out. While this does have some downsides, after all, the softness of the stones does make cave-ins a big risk, thanks to Derinkuyu’s large support pillars, none of its floors have ever collapsed. In any case, while the additions to Derinkuyu effectively ceased after the 10th century, the city continued to be used as a refugee center for the local population during the wars between the Byzantines and the Arabs from the late 8th century to the 12th, during the Mongol raids in the 14th century, and after the region was conquered by the Ottoman Turks.
For the most part, it was only the area’s Greek community that knew about Derinkuyu, but after the Greco-Turkish War between 1919 and 1922 caused all Greek Cappadocians to be expelled from Turkey, the site was forgotten about. It was then rediscovered in 1963 after a local man discovered the city while remodeling his home, and in 1964, it was promptly opened to tourists, and it remains possible to visit the site to this very day.
2. Svalbard Global Seed Vault
If you venture up to the most northern reaches of Norway to the island of Spitzbergen, you’ll come across one of the most important and well-protected underground complexes on the planet. It’s known as the Svalbard Global Seed Vault. It holds a grand total of 1.1 million different types of seeds, with each type being stored in at least a one 500-seed container. In total, 642 million seeds are currently in the vault, and if demand increases, the Vault has the ability to hold two and a half billion.
Of course, this leaves us with an important question: why does Norway have all these seeds in the first place? Well, in essence, the Svalbard Global Seed Vault is like a bank for seeds. All of the seeds are owned by depositors, and generally speaking, these depositors are gene banks who are looking to preserve different seed samples, although at times, various indigenous groups have made use of the vault as well.
The overarching idea behind the seed bank is to preserve the Earth’s biodiversity and have backup seeds ready in case crops or plants in an area are destroyed due to wars, acts of terrorism, or natural catastrophes. When these happen, depositors can withdraw the seeds like one would withdraw money from a bank account, making the whole thing quite streamlined and efficient. Now, in order to keep all these seeds safe, the Vault stores all samples in a series of frozen rooms that are located 120 meters deep into a rock face.
This location helps keep the seeds safe from outside interferences and temperature changes. Although for good measure, the whole facility is strictly climate-controlled and secured, making it a safe place for long-term storage. Yet perhaps the coolest thing about the seed vault is that it’s a humanitarian project. Despite the considerable upkeep cost, the Norwegian government and partner agencies run the global seed bank for free, as all depositors don’t have to pay anything to make use of its services.
In the spirit of humanitarianism, the Norwegian government prioritizes seed deposits that are for agricultural purposes and that come from developing countries, making the vault a tool towards global food and economic security. The end result is a seed vault that not only is comprehensive but has seeds from almost every country, making it an important part of human agricultural heritage. However, it’s because of this that visits are strictly forbidden, although it is possible to get tours to see the outside of the main doors without much trouble.
3. Raven Rock Mountain Complex
If a nuclear World War III were to happen, one thing would be certain: the majority of the world’s population would be toast. However, another certainty is that the same fate would not apply to the President of the United States. That’s because, in the event of another disaster war to strike, he would be able to shelter with the other top political and military officials in a compound known as The Raven Rock Mountain Complex, located high up in the mountains of the state of Pennsylvania.
It was approved by President Truman in 1950 and built between 1951 and 1953 in order to serve as a center of command in the event of a nuclear catastrophe. Pegged the “underground Pentagon,” it’s got Emergency Operations centers for the United States Army, Navy, Air Force, and Marine Corps. In total, it consists of five separate three-story buildings, and these not only contain the basics such as power, water, and air, but also facilitate a medical and dental clinic, fire department, post office, dining facility, snack bar, dormitories, chapel, barbershop, fitness center, bowling alley, and believe it or not, even a Starbucks.
Since two on-site power plants make it completely self-sufficient, it can operate for long periods of time without any outside access. According to the US government, that timeline is a minimum of 30 days in a completely sealed-off position, and in the case of an emergency, a total of 3,000 people can be accommodated within. Of course, this leaves us with one important question: has there ever been an event important enough for the Raven Rock Mountain Complex to actually be used? Well, while there haven’t been any major nuclear attacks since Nagasaki and Hiroshima, 9/11 was pivotal enough for the compound to be used.
While not all officials were whisked away there, Vice President Dick Cheney was housed in the complex away from President Bush, keeping both of them separated and safe in case 9/11 led to a more numerous string of attacks. Thankfully, it hasn’t been deemed necessary to use Raven Rock ever since, although if things keep heating up around the world, Raven Rock may just have to open up its doors once more.
4. Gotthard Base Tunnel
In the past, moving through Switzerland wasn’t all that easy. After all, the presence of the Alps made getting in and out of the country very difficult, while Switzerland’s frigid cold winters could make travel absolutely treacherous. Now, in a way, this was a good thing. After all, having a huge, nearly impassable mountain range more or less surrounding your country makes invasions pretty difficult.
However, in a world where another massive land war in Western Europe seems unlikely, the Swiss have prioritized making their country more accessible. This has been made possible thanks in part to the Goddard-based tunnel connecting the cantons of Uri in central Switzerland and Ticino in southern Switzerland. The tunnel goes directly through a mountain in the direction of the historic Goddard Pass.
For centuries, this pass was one of the only ways to get between Italy and Switzerland, and in 1882, a railway was built across it. This dramatically reduced travel times, and in 1980, things got an even bigger boost when a road in the area made it easier for commuters to get from point A to point B. There, however, by the 2000s, the old and rickety railway had become obsolete, and in order for significant amounts of cargo to once again roll through the area, it became necessary to build a new line.
In 1992, a referendum on whether or not a line, the Goddard-based tunnel, should be built was tabled, and after 64 percent of voters responded yes, the plan went ahead. Built between 1999 and 2016, the nine-billion-dollar tunnel is an incredible piece of engineering, considered to be the world’s deepest and longest underground railway tunnel. It runs for 57 kilometers and reaches a depth of 2,450 meters, making it comparable to some of the deepest mines on Earth.
Since it’s able to handle 160-kilometer-per-hour freight trains and 250-kilometer-per-hour passenger trains, traveling through the tunnel is a breeze, while its horizontal deviation of just eight centimeters and vertical deviation of just one centimeter means that it’s almost perfectly straight, with zero uphills or downhills. So yeah, it is fair to say that the Goddard-based tunnel is one of the coolest railway stretch features ever built.
5. Large Hadron Collider
Now, of all the structures out there, the one that may be just the most useful on this list is the Large Hadron Collider. It’s located on the border between Switzerland and France, near the Swiss city of Geneva. The LHC was quite the project. After all, it took 10 years to build and required efforts of over 10,000 scientists spread across hundreds of universities and labs in over a hundred countries. The result is what we now have as the world’s largest and most powerful particle collider.
But first, what exactly is a particle collider? Well, in short, it’s a machine that allows two subatomic particles to be shot at each other at super high speeds, allowing scientists to record the impact and conduct important scientific experiments. More than 30,000 of these machines exist worldwide, but the Large Hadron Collider is the most incredible of them all. It’s buried 175 meters underground.
It is essentially a 27-kilometer-long circle that’s powerful enough to allow these particle beams to travel close to the speed of light before colliding. This is possible because the entire tunnel is essentially a massive vacuum, and all the strength comes from the tunnel’s magnetic fields. These are created by over 1200 super-strong electromagnetic coils, each of which is 15 meters long and weighs 35 tons.
To make sure that temperatures are optimal for experiments, the colliders are generally maintained at a staggeringly low negative 271.3 degrees Celsius. For reference, this is colder than outer space, and it’s crucial because it allows the magnets to act as effective superconductors, which in turn makes the LHC the incredible tool that it is. Best of all, while the LHC only opened in 2008, it’s managed to facilitate some of the most important scientific experiments to date.
For example, in 2008, the facility was used to create these microscopic black holes that were designed to allow physicists to detect new dimensions. Then, in 2012, it made the real name for itself when it detected the long-sought-after Higgs boson, which was crucial in explaining how particles acquire their mass. It is thanks to these incredible abilities that the Large Hadron Collider is easily one of Europe’s most important modern contributions to the global scientific community.
6. Oppadum
During the Cold War, incidents such as the Cuban Missile Crisis and the 1983 Soviet false alarm brought the planet terrifyingly close to a nuclear World War. It’s because of this that nuclear bunkers were built in order to protect people in a worst-case scenario, and the Oppadum is considered by many to be the best of the best. Located in the Czech Countryside in the proverbial middle of nowhere, it’s not much at first glance from the ground.
Its high walls obstructive view from the air; it simply appears to be a large Administration Center. However, if you go down into its depths, you’ll discover a 323-thousand-square-foot state-of-the-art complex located mostly underground. Now, while there are above-ground apartments so that the residents can live in luxury during times of peace, if crap really hits the fan, they can go down into a state-of-the-art bunker containing multiple high-end apartments in the 8 to 60 million dollar range without upgrades.
The luxury features include an underground garden with simulated natural light, a spa, swimming pool, cinema, library, offices, medical and surgical facilities, and even a custom private vault to store valuables and personal art collections. It will also have an underground control system to maintain communication with the outside world and has multiple high-security systems such as detection sensors, automated defense technology, and blast doors to protect those inside from whatever threat is coming. However, despite the fact that construction began in 1984, it’s still not yet complete.
You see, the idea for the bunker was hatched up at the height of the Cold War, and it was classified as a joint venture between the governments of what were then Czechoslovakia and the Soviet Union. Since the collapse of these states, the Oppadum has become a private venture. Ever since, it’s been in a constant state of construction, and exactly when this will end is still yet to be determined. Yet, when it’s completed, it will undoubtedly be one of the best places to set up shop in case of a massive worldwide disaster.
7. Churchill War Rooms
World War II was a dangerous time to be a Londoner as the constant bombing by Germany during the blitz made living there a life or death situation. As a result, it was decided that Churchill’s War Cabinet, who essentially made all war-related government decisions, would have to move to a secret yet central location. That location was the Churchill War Rooms, located beneath the Treasury building near St. James Park.
Construction began in June of 1938 to fortify the ceilings, install communications and broadcasting equipment, soundproof and waterproof the compound, and put in high-quality ventilation. While the rooms were not perfect, after all, studies showed that a direct bomb hit would have completely polarized those inside. Maintaining its status as top secret on pain of death ensured that those inside remained alive for the entirety of the war.
Consisting of 9,100 square feet of space, the headquarters was staffed at all times and had all the rooms necessary to run a wartime government. For example, the compound was home to the central war room where generals and leading politicians would gather to make decisions, the map room which was an area that was constantly being updated to show the most up-to-date information, communication rooms with telegraphs with direct links to figures like the U.S. President Truman, and office spaces where figures like Winston Churchill would work away in silence.
There were also rooms such as kitchens, reception areas, private bedrooms for top officials, and communal bedrooms for everyone else, making the whole place the epicenter of the British war effort. However, upon losing the general election on July 5th of 1945, Churchill promptly left the war rooms, and once the war was over 46 days later, the entire complex was immediately abandoned. Thankfully, despite the exodus, work was done to upkeep the most important historic rooms, and after a full restoration, the complex was open to the public on April 4th of 1984.
8. Jaylav Air Base
Now, most of the time, airports are firmly on land. However, Jay Lava Air Base is one of the few to be located underground. Built between 1948 and 1968 in the former Yugoslavia, it currently sits on the border between Croatia and Bosnia. By all accounts, it was an incredible feat of military engineering, costing three times the annual military budget of Yugoslavia’s successor states, Croatia and Serbia, combined.
It was built to act as a strategic Command Center in the event of an attack on Yugoslavia by the West. Fit with five runways, numerous defense outposts, and a long-range radar early warning system akin to NORAD, it had all the trappings of a top-tier military base. While everything was underground, it had four exits where Jets could fly out of, and in the case of a nuclear attack, could easily be hunkered down in, able to withstand the force of a direct hit by a Nagasaki-sized nuclear bomb.
It was an absolute unit. While its ability to house up to a thousand people for 30 days in a complete sealed-off environment made it the place to be to protect against nuclear fallout, it was thankfully never used during the Cold War. It soon took on a function that its designers didn’t account for. That’s because, rather than being used for foreign enemies, it became the epicenter of fighting in the Yugoslav Civil War.
While used intensively during 1991 when the Yugoslav People’s Army withdrew from the Arium, they littered the compound with explosives and blew it up so it could no longer be used. While enough explosives were used to incapacitate this structure, it can still be visited today. However, due to unexploded mines, dangerous levels of harmful chemicals, and tensions surrounding the border and refugee crisis, it’s not advisable to go there without a well-thought-out plan.
9. Vivos Europa One
If you’re looking for a top-tier place to hide in style during the next major world war or nuclear meltdown, then Vivos Europa One is the place for you. Built within the bones of a 250,000 square foot Soviet underground complex in Germany, it’s located under a 400-meter-tall hill and is set to provide luxury accommodations to those who live there, while a semi-private room in hostile-like conditions for a total of thirty-five thousand dollars is available for less prestigious clients.
Its set of 34 private 2,500 square foot apartments are reportedly being sold by invite only and only cost 2 million each. These can be stacked up to create two-story 5,000 square foot apartments, and while each apartment will come as a shell, additional features such as pools, theaters, gyms, kitchens, bars, bedrooms, and deluxe bathrooms can be installed on your own dime. Once these spaces are completed, they’ll be entirely closed off so only the owners who want to be there are inside.
However, if you want to enjoy the communal spaces, facilities such as a small zoo, storage for cultural treasures, and a gene bank for reconstituting plants and animals after a possible extinction-level event are all in place. It should also be noted that in case Germany isn’t your ideal choice of location, the Vivos company also has shelters in Indiana and South Dakota. However, if you’re looking for a fully operational shelter in Europe, Vivos Europa is one fantastic option.
10. Strategic Petroleum Reserve
The United States is one of the largest consumers of oil per capita on the planet, with only several small island nations, a handful of Middle Eastern States, and Canada coming out ahead of it. As a result, a strategic petroleum reserve is maintained at all times, with some being let out periodically in order to help ease oil prices in the event of natural disasters and rising inflation. Consisting of a gargantuan 714 million barrels of oil, or about 10 percent of America’s yearly oil consumption, it’s hidden inside a total of four facilities, with two being in Louisiana and two in Texas. It’s here where oil is kept deep underground in storage facilities within salt domes that are highly secured and completely closed off to the public.
