Appearances can be deceiving, even in some of the world's most well-known buildings, stately homes and global landmarks. But if you know where to look, there's a treasure trove of secret passageways hiding in plain sight, facilitating sanctuary, escape and more curious goings-on.
From Capitol Hill and London's House of Commons to the Palace of Versailles, Dracula’s Transylvanian castle and El Chapo's covert safe house, click or scroll on to discover the world’s most incredible hidden passages and tunnels.
As strange as they are mysterious, Erdstall tunnels can be found across Europe, mainly in south-eastern Germany in the state of Bavaria and in Austria. But why were they made and what were they used for? Well, those are two questions that have stumped historians. Erdstalls are thought to have been crafted during the Middle Ages, though some have claimed that they date back to the Stone Age.
So, all we really know is that they were constructed somewhere between 5,000 and 12,000 years ago. Generally, these tunnels are very low and narrow, oval in shape and extend between 65.6 feet (20m) and 164 feet (50m). Even more strangely, many of the tunnels are extremely tight, around just 1.3 feet (40cm) in diameter, making it impossible for humans to traverse them.
We may never truly know why these strange passageways exist, but some have suggested one network stretches from Scotland to Turkey, although no evidence has proven this. Scientists also suggest that they might have been used as secret spots to hide out in during periods of war or conflict.
Erdstall is derived from German and can be roughly translated to ‘earth stable’ or ‘mining tunnel’, so perhaps these hidden underground spaces were used as shelters or mine shafts. At present, around 2,000 erdstalls are known to exist in Europe, but we're sure there are many more lurking beneath the earth...
From subways to water channels, the Spanish capital of Madrid is thought to be home to around 2,485 miles (4,000km) of underground roads, tunnels and passages. Yet none of them are quite so interesting as the Túnel de Bonaparte – AKA, the Tunnel of Bonaparte.
Seen here from the outside, the underground passageway was crafted for Joseph Bonaparte, who at the time was the reluctant King of Spain. He was much hated by the people of Spain, who saw him and his French troops as oppressors, according to Fascinating Spain. Fearing for his safety, the monarch needed a way to get between the Royal Palace and his residence, Casa de Campo, without being seen or attacked.
The tunnel project was handled by distinguished royal architect, Juan de Villanueva, who is said to have been a "master of the neoclassical style". He designed a simple tunnel, stretching more than 164 feet (50m). It was constructed in 1811 and ran between the Campo del Moro palace gardens and Casa de Campo. After Joseph I fled Madrid, the tunnel went on to serve the new monarch, Ferdinand VII, who is considered to be one of the most heinous kings to ever sit on the Spanish throne.
In 1931, Casa de Campo became an urban park and the Bonaparte Tunnel was opened to the public. However, with the construction of a motorway in the 1970s, the tunnel was closed once again, with just a commemorative plaque left marking its location and history.
The seat of the US government, Capitol Hill is a vast complex that encompasses the Capitol Building, the US House of Representatives, the US Senate buildings and the Library of Congress. While it's a hive of activity above ground, the same can be said for the Capitol's secretive subterranean world too.
Beneath this hub of American politics lies a sprawling network of covert tunnels that run between the various governmental buildings, offering a safer and more efficient way for political movers and shakers to navigate the complex.
The tunnels include the Capital's private subway system, the chosen mode of transport for politicians, Supreme Court justices, presidents and world leaders. The little-known line was originally constructed in 1909 to link the Russell Senate Office Building to the Capitol and provide safe travel for members of the Senate and Congress from their offices to voting chambers.
The first iteration of the subway was serviced by cars, but fast-forward more than a hundred years and an automatic train now ferries members of America's political parties to and fro. As of today, the subway has grown to include three lines: two routes on the complex's north side where the Senate is located and one on the south side to cater to the House of Representatives.
One of America's largest historic homes, Lynnewood Hall in Philadelphia, Pennsylvania has been dubbed the "last American Versailles", thanks to its breathtaking neoclassical architecture. The 480-acre (195ha) Gilded Age estate was completed in 1900 for business mogul Peter A B Widener, who would go on to lose both his son and grandson on the RMS Titanic in 1912.
Tainted by tragedy, the house passed between numerous hands over the years before being left to languish for over a decade. However, the building's staggering beauty has endured.
The mansion still has one or two secrets kept close to its chest too. Beneath the faded grandeur and vestiges of the past lies an underground warren of tunnels that helped this vast property run like clockwork during its heyday...
When photographer Leland Kent of Abandoned Southeast toured Lynnewood Hall in 2021, he stumbled upon the entrance to a remarkable underground tunnel system nestled deep in the home's basement. Strewn with debris, the passages branch off in multiple directions, perhaps offering a way for the mansion's army of staff to navigate the house out of sight of the Wideners. It's thought that the tunnels may have housed the estate's plumbing and drainage systems, too.
More secrets about this enigmatic stately home may yet come to light, as the property was purchased in 2023 by the Lynnewood Hall Preservation Foundation, who intend to restore the mansion to its former glory.
It's one of London's most fiercely guarded buildings, however, a shocking discovery was made in the House of Commons during a restoration project in 2020. Unbeknown to security staff, a secret passageway lurked beneath the building's historic, wood-panelled walls.
According to archival documents, the 360-year-old passage was created for the coronation of King Charles II in 1660 to allow guests access to the adjacent Westminister Hall, where the coronation banquet took place.
For a time, it was used as the main entrance to the House of Commons and it's thought that many illustrious names in the world of politics passed through the secret tunnel, including famous diarist Samuel Pepys.
However, the entrance to the thoroughfare was bricked up in 1851, although the passageway was left intact. The 19th-century workmen tasked with the job left behind details of their lives graffitied on one of the walls, traces of which can still be read today, according to ITV News.
The parliamentary passage was briefly rediscovered in 1950 when the building underwent repairs following bomb damage from the Second World War, however, it was resealed and forgotten about until historians uncovered it once again in 2020.
Beneath the leafy squares of Lyon's La Croix-Rousse neighbourhood, unbeknown to its residents, lies one of the French city's most perplexing architectural mysteries: the Fishbones. A network of 32 parallel stone-lined tunnels, its name derives from its strange structure, which resembles a fish skeleton.
Discovered by municipal workers in 1959, the ancient complex was initially kept secret from the public and the tunnels have remained closed since they were uncovered. Today, the underground network is accessible via manholes, though there's also thought to be a historic entrance concealed within Lyon's Saint Bernard church.
The purpose of the tunnels remains shrouded in mystery to this day – most puzzling of all, each identical 100-foot-long (30.5m) tunnel leads to a brick wall, giving rise to a whole host of theories.
The origins of the subterranean passageways are no clearer. While a 2013 archaeological study dated the complex to before the Middle Ages, Walid Nazim, author of The Secret of Lyon's Fishbones, believes the tunnels could have links to the last Grand Master of the Knights Templar, William de Beaujeu.
According to Nazim, Beaujeu owned the land on which the Fishbones was built in the 13th century. The author thinks it's possible that the complex was used as a safe to store Templar treasures. Whatever the truth, this is one architectural mystery that may never be solved.
Once protected by the Official Secrets Act, this maze of mile-long tunnels beneath central London was originally constructed in the 1940s as a bomb shelter. Sequestered 131 feet (40m) beneath Chancery Lane tube station, the fortified tunnels sheltered Londoners from the onslaught of the Blitz.
The tunnels were then closed to the public and repurposed as a base for British Prime Minister Winston Churchill's Special Operations Executive, a covert offshoot of MI6 tasked with destroying German infrastructure from behind enemy lines. It's also thought to be the real-life inspiration for James Bond's Q Branch.
During the Cold War, the tunnels were reinvented once more as the Kingsway Telephone Exchange. The clandestine centre facilitated internal communications during the tumultuous period, as well as hosting a secret hotline that directly connected US President Eisenhower and Russian Premier Krushchev.
Decades later, the secure complex was bought up by British Telecom in the 1980s. In contrast to its utilitarian past, the company installed the world's deepest licensed bar at the time for its staff, as well as a games room and a tropical fish tank.
Decommissioned in the late 1980s, plans are now afoot to transform the tunnels into an underground tourist attraction.
A hidden subterranean world lies under the ground in an unassuming, rural spot near the Polish town of Międzyrzecz, an area that was part of Germany until the Second World War.
Following Hitler's rise to power, work began on a system of fortifications in 1934 that would form one of Nazi Germany's key military defence lines. A network of bunkers and observation posts was constructed, connected by a vast web of interconnected tunnels, reportedly stretching around 25 miles (40.2km) long and descending to a depth of 131 feet (40m).
Camouflaged in green paint, an entrance to the underground is pictured here, partially submerged beneath the earth.
The tunnels were equipped with workshops, storage areas, generators and barracks for troops. They also contained underground train stations – many of the passages were equipped with tracks that would carry trains filled with soldiers, weapons and supplies to the bunkers along its route. The complex has been described as Nazi Germany's secret underground city.
Following the end of the Second World War, the sprawling fortifications and tunnels were abandoned and left to languish. The derelict structure is now said to be one of the largest underground nature reserves for bats.
Today it’s a popular tourist attraction drawing thousands of visitors a year, but Passetto di Borgo was originally built as a secret escape passage for the Pope, allowing him to flee from Castel Sant'Angelo into Vatican City.
The passage itself is an elevated, 2,624-foot-long (799m) corridor concealed within what otherwise appears to be an old fortified wall. It was initially constructed in 1277 by Pope Nicholas III, but was expanded to its current form by the Borgia Pope Alexander VI in 1492.
At least two popes have used the passage to escape danger. The first was Pope Alexander VI in 1494, who used it to flee when Charles VIII invaded the city and threatened his life. The second was Clement VII during the 1527 Sack of Rome when the city fell to Holy Roman Emperor Charles V and his troops.
Though the passage has not been used since and indeed languished in a state of disrepair for many centuries before its renovation in 2000, the Swiss Guard reportedly keeps a key on hand for the Pope, just in case…
The Gilded Age centrepiece of Times Square, the Knickerbocker Hotel is a Beaux-Arts masterpiece that belonged to one of the first American millionaires, John Jacob Astor IV. The hotel itself was built in 1906 and had 500 rooms, multiple restaurants and a magnificent bar where it is rumoured that bartender Martini di Arma di Taggia invented his namesake cocktail.
While most visitors entered the bar through the main doors in the hotel lobby, for those in the know, there was a more secretive way in…
Deep below the streets of Manhattan, at the far end of the platform of Track 1 on the S shuttle between Grand Central and Times Square-42nd Street, closest to the 42nd Street exit, a white utility door goes largely unnoticed by most passers-by.
Only the brass plaque reading ‘Knickerbocker’ indicates that behind this door lay the secret entrance to the hotel bar, perhaps designed for VIPs looking to fly under the radar. While the door remains to this day, the passage is no longer accessible. After closing down in 1920, the Knickerbocker Hotel reopened under its original name in 2015.
During the Vietnam War, this network of secret tunnels below the jungles of Củ Chi District was used by Communist guerilla troops, referred to as the Viet Cong, as supply routes, hiding places and living quarters.
The labyrinthine tunnels allowed resistance fighters to operate covertly out of the firing line of American and South Vietnamese enemy forces and connected Ho Chi Minh City with swathes of the rest of the country.
During periods of heavy fire, Viet Cong soldiers frequently needed to stay below ground for days at a time, rationing resources as best they could. Life in the tunnels was incredibly difficult because food and water were scarce, insects and vermin were plentiful and disease was rampant.
The tunnels have been preserved over the years and are now open to the public, enabling visitors to imagine what life would have been like for the soldiers living and fighting there.
Marie Antoinette was notorious for her love of excess, opulence and luxury – proclivities that contributed to her untimely passing.
Dripping with gold, her private apartments in the Palace of Versailles epitomise these tastes and were designed to wow the audiences she was expected to host there, including during such intimate moments as the births of her children.
But when she really needed some time for herself, the queen had the perfect secret escape…
Built into the tapestried panel of the wall beside Marie’s bed, a nearly invisible door opens into the French queen’s truly private sanctuary, a set of rooms where she could retreat from both court and her husband with select members of her entourage.
Among the suite of rooms were a library, boudoir and lounge, all as opulently appointed as her main bed chamber. When the people marched on Versailles during the French Revolution in 1789, it is believed that the queen was discovered hiding in these rooms with her children.
The suite has recently reopened to the public after a prolonged period of careful restoration.
This mighty monolith is probably Gibraltar’s most famous attraction, but what many people don’t know is that you can actually go inside the Rock of Gibraltar thanks to a network of tunnels so extensive and spacious that they’ve been likened to an underground city.
The tunnels were dug during the Second World War at the behest of Winston Churchill, when Gibraltar became a strategic choke point between German-dominated Europe and the sea. They were designed to act as storage facilities for vital supplies, as well as siege accommodation for troops.
The passages were dug by four specialised tunnelling companies from the Royal Engineers and the Canadian Army.
When they were complete, the top-secret bunkers were capable of housing a 16,000-strong garrison, as well as enough food, equipment and medical supplies to last for 16 months. More impressive still, the tunnels also housed a telephone exchange, a power generating station, a water distillation plant, a hospital, a bakery and a vehicle maintenance workshop.
Today, the tunnels are open to visitor tours and are one of Gibraltar’s most popular tourist attractions.
Concealed in the belly of Slovenia’s Predjama Castle, the world’s largest cave castle, this secret network of underground passages once played a crucial role in keeping a 15th-century rebel knight fed and watered as he waited out his persecution.
Six centuries later, the castle is now open to the public, allowing visitors to follow in the footsteps of this renegade knight.
The castle itself dates back to the 13th century, but in the 1400s it was under the ownership of Erasmus of Lueg, who used it as his refuge after he fell foul of the Habsburg rulers of the region and was deemed an outlaw for his raids on the district's towns.
Habsburg forces surrounded the castle, expecting Erasmus would surrender when his stores ran low. Little did they know that below the castle, a secret network of tunnels enabled Erasmus to come and go freely between the castle and a local village that supplied him with as much food and wine as he wanted. The siege eventually ended when Erasmus was reportedly betrayed and assassinated.
The Portuguese palace of Quinta da Regaleira hides a rather unusual architectural feature – two initiation wells plunging 88 feet (26.8m) below ground, each encircled by a gothic spiral stone staircase to create an enormous subterranean tower.
Descending into the wells, there's a tiled floor at the bottom decorated with the symbols of the Knights of Templar, which could explain why these wells are believed to have been the sites of covert initiations into secret societies…
Arguably eerier still is the network of winding cave tunnels that lie beyond the wells. These rough-hewn passageways seem like a natural occurrence but they're man-made.
A relatively recent construction, the mysterious palace was completed in 1910 for eccentric Freemason António Augusto de Carvalho Monteiro, who set about filling the gothic castle with symbols of Freemasonry and the Knights Templar to reflect his esoteric interests.
While the exterior of this Transylvanian castle may look like something straight out of a fairytale, its interior is even more fantastical. Bran Castle, as the monument is known, was the site of many battles throughout history and is rumoured to have been the prison of the notorious Vlad the Impaler.
Some even think the fortress was the inspiration for Dracula’s castle in Bram Stoker’s gothic horror novel. Perhaps it is no surprise then that the castle comes with a secret escape route...
Concealed within a wall and disguised by a fake fireplace, the entrance to this staircase was so well hidden that it was forgotten for decades. It was only rediscovered when Queen Marie of Romania, granddaughter to Queen Victoria, set out to renovate the room into a parlour.
The staircase was believed to have been built as an escape route for the castle’s inhabitants in case of invasion. Today, it is on display to visitors and remains one of the famous castle’s main attractions.
One of the most infamous drug lords of all time, El Chapo was worth billions of dollars at the time of his capture by US authorities in 2016.
Despite his immense wealth, however, the cartel boss spent most of his time hiding out in comparatively modest safe houses, such as this one in the quiet Culiacán neighbourhood of Libertad in Sinaloa, Mexico. But while the home itself was unassuming, it was kitted out with a pretty high-tech escape route hidden beneath the bathtub.
El Chapo fitted the tub with a hydraulic system that enabled it to be raised at lightning speed, providing access to an escape tunnel connected to the local sewage system.
It was through this tunnel that the drug lord escaped with his mistress and maid when law enforcement descended on the house in 2014, only to be apprehended and finally arrested by Mexican marines a few days later.
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