From the perplexing wonders of the world to modern structural oddities, there are plenty of architectural mysteries out there that have long gone unexplained.

From baffling buildings to hidden cities, these enigmas are plagued by unanswered questions. Why are they there? Who put them there? And why is there so much intrigue shrouding them? 

Click or scroll on to get to the bottom of these architectural puzzles once and for all...

Perched on a rocky outcrop in the heart of the Pyrenees mountain range, Château de Montségur stands at an altitude of 3,960 feet (1,207m). The unusual castle has a complex history, but it's also shrouded in folklore and mystique. 

At the beginning of the 13th century, a unique religious group settled in the area and the castle quickly became the seat of the Cathar church. Sadly, in 1243, the Pope and the King of France decided it was time to end the religion. After a near year-long siege, more than 200 Cathars were put to death after refusing to renounce their faith...

During a 15-day truce, a few people escaped the castle and are said to have taken Cathar treasure with them. German archaeologist Otto Rahn also believed the Holy Grail, a goblet with miraculous healing powers, was kept in the castle. Excavations were carried out, but no treasures have ever been found.

In addition, the castle experiences a rare solar phenomenon during the summer solstice; a ray of sunlight passes through two archways in the fortress wall, which appears to split the château in two. While the sun was used as a landmark for many ancient builders, it's a magnificent spectacle for all who gather to witness it.

Located in the state of Rio de Janeiro on Brazil's Costa Verda lies the colonial town of Paraty. Entering the quaint community is like stepping back in time to the 18th century – the streets are lined with whitewashed buildings and cobbled streets, virtually untouched since their construction. 

Yet the town's old-world charm isn't what makes this settlement one of the most mysterious locations in Brazil. If you look closely at the architecture, you might notice columns of strange symbols enveloping the buildings...

These odd markings aren't merely decorative – they're geometric ciphers left by the town's creators, the Freemasons. In fact, Masonic symbolism is imbued into every aspect of Paraty's design. The streets are structured as a grid of 33 blocks, a sacred Masonic number, and 33 councilmen once oversaw the running of the community.

The Freemasons who established Paraty had escaped persecution in Europe and fled to Brazil, which was under Portuguese rule in the 18th century. No longer endangered by their beliefs, they built an overt homage to the secret society that continues to be preserved to this day.

In the winter of 1850, a violent tempest hit the northeast coast of Scotland and revealed an archaeological mystery. Villagers on the Orkney mainland woke up to find that layers of sand had been blown away, leaving the outline of several small houses.

It wasn't until the late 1920s that serious work began on the site, which is known today as Skara Brae. Eight neolithic dwellings were eventually uncovered, dating back to around 3180 BC. Each home was built from stone slabs, which were set into middens, or large refuse heaps. They were linked by covered passageways. Consisting of a single room, the houses contained 'fitted' stone dressers and beds, as well as a central hearth for a fire. 

Jewellery, pottery and tools were found in the homes, indicating that the people of Skara Brae were farmers, hunters and fishermen. So why did they leave the settlement after 600 years, seemingly in a hurry?

Around 2500 BC, the climate grew colder and wetter, making the tiny coastal village a less desirable place to live, while encroaching dunes gradually covered the homes until they became uninhabitable. Today, the incredible dwellings are a UNESCO site and make up Europe's best-preserved Neolithic Age village.

One of the new seven wonders of the world, the ancient city of Petra was once the capital of the Nabataean kingdom between 400 BC and AD 106. Carved into the red sandstone cliffs in Jordan, Petra's extraordinary buildings were 'lost' to the Western world until the early 1800s.

Many of the stone structures are simply façades hiding burial chambers inside, leading early explorers to conclude that Petra was a puzzling city of tombs. However, modern findings point to a thriving trade centre with elaborate terraced gardens, pools, spas and villas. A grand free-standing temple complex with a 600-seat theatre is just one of the discoveries..

It's estimated that around 30,000 people lived here at its peak, surviving the hot summers by channelling winter rain into hundreds of vast rock cisterns that the Bedouin still use today.

As for why the ancient city was abandoned, it's no longer a mystery. New trade routes took business from the area, but the final blow came in AD 363 when a massive earthquake destroyed almost half of Petra. However, scholars argue that Petra was never truly abandoned at all and that the valley has continued to be inhabited and farmed over the centuries. Intriguingly, only 15% of the city has been uncovered. The vast majority still lies beneath the surface, waiting to be discovered...

Rising up among rolling, pastoral fields, this curious concrete structure with its metal, triangular door looks somewhat otherworldly. The landmark is located in the German town of Mechernich in North Rhine-Westphalia and has been described by onlookers as an "extraterrestrial monolith", as though it were dropped there by aliens.

Its construction is equally unusual. The building was formed by 112 tree trunks leant together to create a wigwam. The structure was then encased in 24 layers of concrete before the wooden frame was set alight, charring the interior.

You can see the blackened, ash-stained walls here, imprinted with strange markings from the flames. Despite its eccentricities, the monolith is entirely the work of planet Earth between 2005 and 2007. It was designed by Swiss architect Peter Zumthor at the behest of a group of local farmers who wanted to create a shrine to the patron saint of Switzerland, Nicholas of Flüe – also known as Bruder Klaus.

The chapel features a teardrop-shaped opening at its peak, exposing the interior to the sky and the elements and the floor is coated in a layer of cooled molten lead.

With its two craggy rock formations protruding toward the clouds, Waqra Pukará, which translates to horned fortress, is one of Peru's most perplexing sites. While it's often overshadowed by neighbouring Machu Picchu some 80 miles (130km) away, the ancient site is one of the country's hidden historical gems.

Despite the site's sheer scale, little is known about it. The terraced rock has obvious parallels to the Incan Empire, yet archaeologist Oscar Montúfar told the BBC that there is archaeological evidence tying the locale to earlier cultures, including the Pukará civilisation, which flourished between 1400 and 550 BC. Signs of the Tiawanaku, Wari, Canchis and Inca civilisations are also evident. But what was the site used for?

The remnants of structures we see today date back to the Inca period, according to Montúfar. But despite being known as the horned fortress, he believes the site wasn't a military fortification or a residential settlement. "When the Inca came to Waqra Pukará, they designated it a sacred place, but it was used for ceremonies and pilgrimages with pre-Inca cultures as well," Montúfar told the BBC. 

One crucial indicator of the site's spiritual significance was the detailing of the door frames. Each was fitted out with a triple jamb – three recessed frames nestled into each other. This architectural feature was only used for the culture's most hallowed buildings. Even Machu Picchu doesn't have this type of revered detailing.

The historic Cappadocia region in Turkey is steeped in ancient wonder and home to an unbelievable number of fascinating underground cities, the largest of which is the multi-level Derinkuyu.

Descending over 200 feet (61m) underground and reportedly accessed by hidden doors in the courtyards of ground-level homes, the city is said to have been large enough to house around 20,000 residents in its heyday. It's said to have had a wide array of amenities, including stables for animals, churches and a school built underground.

But how did this ancient subterranean site come to be? The answer is rather surprising...

The city was discovered in 1963 when one man knocked down a wall in his basement while renovating his home and discovered a mysterious tunnel network. This was eventually revealed to be the ancient city of Derinkuyu, a subterranean warren 18 storeys deep. Purportedly created around the 8th or 7th century BC, archaeologists think that the caves were carved by hand into soft volcanic rock.

Derinkuyu is now open to the public to explore, although only about 10% of the city has been made accessible to visitors. We can’t quite believe the secret city was hiding just behind someone’s basement wall!

While some theological tableaus date back to ancient times, the Georgia Guidestones were erected in 1980 but are no less mysterious. The American version of Stonehenge is made up of vast granite slabs, measuring 16 feet tall (4.9m) and weighing 119 tons (108t). Inscribed in eight languages – one for each stone – is what appears to be a 10-step Armageddon guide in English, Spanish, Swahili, Hindi, Hebrew, Arabic, Chinese and Russian.

The mystical monument was commissioned by someone using the pseudonym Robert C Christian on behalf of an anonymous "small group of loyal Americans".

Conspiracy theorists have long been vocal in their distrust of the monument and it was mysteriously bombed on 6 July 2022 by unknown individuals. Despite a surveillance camera capturing the explosion and a silver saloon car leaving the scene, the perpetrators and their motives remain a mystery.

After assessing the damage, the Georgia Bureau of Investigation (GBI) decided to demolish the stones "for safety reasons”. America's Stonehenge may have fallen, but the reason why this monument appeared and why it was destroyed are mysteries that may never be answered.

While these unusual-looking staircases may cause some raised eyebrows these days, they were all the rage in 17th-century New England, causing many to believe that the stairs' origins were associated with the Salem Witch Trials.

Many old New England homes still feature these alternate-tread staircases, also known as witches' stairs. An urban myth arose suggesting that the stairs originated from the belief that witches were unable to climb them and were, therefore, a means of protecting the household.

The myth has since been debunked, and it turns out that alternating tread staircases were just a means of saving space in smaller homes, cleverly reducing the footprint of a staircase by half while providing a more stable alternative to rickety ladders. 

Indeed, for this reason, alternating tread staircases are still a popular choice in smaller apartments for accessing lofts or raised mezzanines. While they may not ward off witches, they do at least optimise space!

It may look like a cupboard or secret storage space, but this hiding place was one of many found in stately homes across the UK. They are, in fact, priest holes used to conceal Catholic clergy during the English Reformation of the 16th century. Almost overnight, Elizabeth I had made it illegal to be a Catholic, but many devout families continued to worship in secret.

This priest hole is hidden away in Harvington Hall, an Elizabethan manor house in Worcestershire, England. Known as the "House of Secrets", the historic home has seven different priest hides, more than any other house in the country.

These priest holes in Baddesley Clinton, Warwickshire, hid Jesuit priests during a notorious raid. The one on the left is accessed via a concealed shaft in the toilet that leads into the medieval sewers, while entry to the one on the right is via a hidden opening in the kitchen.

Jesuit priests were sent over from the continent to secretly serve the wealthy Catholic families that remained in England. Often posing as a distant cousin or relative, they would perform mass and other religious services with small portable altars at great personal risk. 

Have you ever found yourself in an awkward situation when you wanted the ground to swallow you up? Maybe a spiralling staircase underneath a pavement hatch will do the trick.

With a futuristic spaceship-like entrance, this manhole in Wiesbaden, Germany, invites passersby to take the plunge and venture down underneath the city streets.

Down the rabbit hole, you’ll discover the science-fiction contraption is really the entrance to the dungeon of the Salzbach canal – one of the oldest in central Europe.

A maze of shadowy tunnels running beneath Wiesbaden, most pedestrians above ground have no clue about the subterranean world lurking beneath their feet.

Perhaps the world’s most famous, ancient and elusive architectural mystery is that of the pyramids of Giza in Egypt. Built around 2500 BC as colossal tombs for the great pharaohs, it’s not their existence that’s necessarily perplexing, but how they were built.

In an era predating industrial revolutions and modern mechanics, the colossal blocks of stone seem impossible to manoeuvre without the technology of today.

The topic of much debate among archaeologists, a likely explanation for the pyramids' construction has come to light in the past few years. While researching ancient inscriptions on the Giza monuments, scientists came across a ramp with stairways that could've helped to haul the stone into place.

A series of postholes were also discovered and are thought to have formed part of a pulley system used to lift blocks, getting the stone into place far quicker than experts initially thought possible.

Tara National Park in Bajina Basta, Serbia, has long drawn tourists from around the world, but the origins of the Drina River House, balanced precariously on the edge of a rock, remain murky to many.

The first version of the house was thought to have been built by a young group of swimmers in the 1960s and it became their annual summer house by 1969 – a place to rest and shelter from the blazing sun.

Upkeep was constantly required as river levels would frequently rise and damage the structure of the house, so materials to maintain the building had to be transported across by boats and kayaks.

Unbelievably, the house is still standing today and is the prized centrepiece of the annual Drina Regatta.

There’s so much intrigue surrounding Göbekli Tepe, an ancient Turkish archaeological site home to the oldest temple structures ever discovered. Excavations began in 1995 near the city of Şanlıurfa, unearthing ruins believed to date back to between the 10th and 8th millennium BC.

During the first phase of excavation, gigantic T-shaped stone columns were discovered, weighing more than 16 tons (14.5t).

Experts say the site predates the invention of agriculture and pottery, refuting the assumption that agriculture led to the beginnings of civilised society as we know it.

More than 200 pillars in around 20 circles have already been uncovered, revealing distinctive room-like structures. While their precise use is as yet unknown, UNESCO believes they were probably used in connection with funerary rituals.

Sitting on the outskirts of Cusco, the historic capital of the Incan Empire, Sacsayhuamán is so mysterious that there isn’t even an agreed formal spelling – some opt for Saqsaywaman instead.

Thought to mean 'Royal Eagle', Sacsayhuamán still baffles archaeologists to this day. Similarly to the pyramids, how the structure came to be remains largely shrouded in mystery.

Dating back to around the 15th century, the structure is believed to be part of a fortress-temple complex, its stonework resembling a giant game of Tetris, with stones expertly carved and slotted together – incredibly advanced for the age.

Large in scale, architect John McCauley thinks that the lighter stones could've been dragged over carefully prepared soil beds to the site, while heavier rocks may have been transported via sled. 

Given the historic Salem Witch Trials, it's no surprise that the East Coast of North America was paranoid about witches, but who knew this fantastical fear would bring about a peculiar architectural phenomenon? Almost exclusively in Vermont, you’ll find what’s known as witch windows.

Folk tales stipulate that witches can’t enter diagonal windows on their broomsticks, leading residents to install slanted windows into the sides of their homes as a preventative measure.

The design is also known as a coffin window because, according to old wives’ tales, they were used to remove coffins from the second floor in order to avoid narrow staircases.

However, witch windows are most likely explained by a third, more boring theory: vernacular Vermont architects simply wanted to draw light and air into tricky attic spaces.

High-altitude homes don’t come much more extreme than the Katskhi Pillar: a 130-foot-tall (39.6m) stone column with sweeping views of the western Georgian region of Imereti.

Atop the remote pillar sits an ancient church, burial chamber and cottage. From the early 1990s, it was home to just one resident, Father Maxime Qavtaradze, who lived as a stylite – a spiritual person who lives alone on an elevated pillar as a demonstration of their devotion.

At the foot of the column, there’s a monastery where priests and troubled men seek solace. A few times a week, Father Maxime travelled down the connecting ladder to offer guidance to the people at its feet, but the monks also sent him supplies via a pulley system, as well as making the daily climb up to the church for prayer and worship.

Father Maxime came down from his pillar for good in 2015 and became the leader of the Katskhi Monastery below.

While signs of civilisation in Bolivia's Tiwanaku region are thought to date back to 536 AD, the enigmatic Puma Punku temple complex suggests habitation of the site goes back much further; in fact, it's purportedly almost 14,000 years old.

Puma Punku was said to be especially important to the Incas who believed it to be the spot where the world was created.

The complex encompasses western and eastern courtyards, a central esplanade and a stone-faced terrace platform. Once thought to have been adorned with precious materials, including polished metal plaques, kaleidoscopic ceramics and elaborate fabrics, the temple was purportedly frequented by the ancient society's upper echelons.

While much is unknown about its construction, two commonly accepted theories suggest the stones were moved using llama-skin ropes or ramps.

Found in the UK's East Midlands region, this regal deconsecrated chapel sits on the edge of one of Europe’s largest man-made lakes, though its precarious location might make you look twice.

When the tide is high, the church seemingly floats, but when the water level drops, the lower half of the church appears to sink into the rocks.

In reality, the church is a spectacular optical illusion conceived by Thomas Cundy Jr in the early 19th century. Now a popular wedding venue, Cundy based the design on the church of St John's Smith Square in London's Westminster, but where he got the idea for the mirage is unknown – it may not even have been intentional.

Wandering along Amsterdam’s innumerable waterways, you may find yourself in the canaled city’s Jordaan neighbourhood. Counting down the house numbers on the north side of Westerstraat, you'll find that there are seven missing addresses. But if you look closely, you'll spot the seven missing houses stacked one on top of the other in the nook between the two buildings.

Way back when, there was an accessible courtyard through a low door that would lead to the seven full-sized missing houses, but in their absence, their miniature models continue to delight eagle-eyed visitors.

So, how did these whimsical homes end up here? They were installed by a local advertising agency based in the building.

If building huge stone temples and monuments above ground wasn't tough enough, some may have taken their construction efforts underwater, or so marine geologist Masaaki Kimura has alleged.

In 1986, divers discovered a curious submerged rock formation off the coast of Yonaguni Jima, the southernmost of the Ryukyu Islands in Japan.

Kimura says each time he returns to the site, he's even more convinced that the formation, which he describes as containing a stepped pyramid, is that of a 5,000-year-old city.

Whether it's natural or artificial is a hugely divisive topic, with some expeditions attributing the etched drawings to no more than natural scratches on the stones. However, their seemingly purposeful assembly could lead one to believe this was no force of nature.

A unique example of novelty architecture, this supersized basket has been baffling passersby in Newark, Ohio, for years.

When Dave Longaberger, founder of basket manufacturers the Longaberger Company, instructed architects to design the brand's headquarters in 1997, he's said to have pointed at their best-selling product, the Medium Market Basket, and said: "make it look exactly like that”.

True to his vision, the result is a surreal seven-storey, 180,000-square-foot (16,722sqm) office that looks uncannily like a basket.

The building was sold in 2017 to an Ohio-based developer, and in 2019, it was opened to the public for tours, with lines of visitors perplexed by the basket's surprisingly grandiose interiors. However, according to some reports, the structure is now abandoned as the new owner pursues options for its future development.

Rising above the skyline of Florence, the distinctive dome of the Cathedral of Santa Maria del Fiore is one of the ancient city's most iconic sights, and it's also the most intriguing. Created by goldsmith Filippo Brunelleschi in the 15th century, the vast cupola comprises an inner shell and an outer shell, plus precise herringbone brickwork.

Built without flying buttresses or scaffolding, the architectural marvel has left architects and historians puzzling over its construction for centuries.

Architect Massimo Ricci, who has dedicated much of his life to the quandary of the cupola's creation, may well have uncovered the answer.

By carefully mapping the dome and building scale models to test his theories, Ricci arrived at a likely explanation – according to his calculations, a complex system of chains, hooks and ropes would've allowed the careful construction of the breathtaking octagonal space.

Perched among the peaks of Peru's Andes Mountains, the ruined city of Machu Picchu is believed to have been built in the 15th century at the height of the Inca Empire.

Stretching over five miles, the site, which is flanked by steep drops on three sides, is elevated a lofty 7,972 feet (2,430m) above sea level, prompting geologists to question why such a remote and inaccessible spot was chosen. The reason may just lie underground...

Positioned on a unique spot where two tectonic plates meet, the faultline produced large amounts of stone over millions of years, offering the Incas plentiful building materials for their new city in the sky.

According to geologist Rualdo Menegat, this convenient abundance of stone, as well as the natural drainage offered by fractures in the rock, was likely an important factor in the site's selection, aiding the construction of the settlement's intricate and advanced structures.

Dating back to around 2500 BC, Stonehenge is still considered something of an ancient enigma. Comprising a number of towering stone settings arranged in a circle, the mysterious site in south-west England is remarkable in its scale and age, causing many to wonder how the enormous stone monument was built and, more intriguingly, why.

There's no end of theories out there about the circle's purpose, from a Druid temple to an astronomical computer for predicting eclipses.

However, according to English Heritage, the most accepted explanation of Stonehenge is that the structure was created as a prehistoric temple, aligned with the phases of the sun.

With some of the stones traced to a Welsh quarry some 140 miles (225km) away, scientists at Newcastle University think the large settings could have been transported using sleds greased with pig fat, after residue was discovered on ancient pottery shards found near the site. Well we weren't expecting that!

This grand 19th-century mansion in San Jose, California, has long beguiled and baffled the public. Listed on the National Register of Historic Places, the Winchester Mystery House is a maze of winding corridors, twisting staircases and doors that lead to nowhere – just imagine the nasty surprise you'd get if you walked through the door above and encountered that eight-foot (2.4m) drop!

But how exactly did this seemingly nonsensical home come about?

Once an ordinary eight-bedroom farmhouse, the home was bought up by Sarah Winchester, the heir of a weapons manufacturing company, who relocated to the area after the deaths of her husband and son. Perhaps consumed by grief, she began to remodel the house, adding more wings, corridors and secret passages.

Legend has it that Sarah believed she was haunted by the spirits of those killed by her family's weapons, so she built false doors and staircases leading to the ceiling to confuse malevolent ghosts.

An Italian icon, there are few structures more instantly recognisable than the Leaning Tower of Pisa. Throughout the decades, Italy has been hit by its fair share of devastating earthquakes, yet somehow, this precarious 183-foot-tall (55.8m) landmark has endured it all.

According to engineers from the University of Bristol, the secret behind its surprising resilience lies in the ground...

Funnily enough, that soft foundation soil that caused the tower's famed tilt is also responsible for protecting the structure from earthquakes for all these years.

The tower's height, combined with the stiffness of the marble and the soft soil, ensures vibrations are absorbed differently than in typical buildings, allowing the historic wonder to remain standing all these years!

Novelist and PhD student Paul Cooper noticed something very odd about this picture of the fabled Temple of Zeus from 1860. At the top of the pillars, there appears to be a small building.

Constructed in the 6th century BC, the temple is one of the jewels of Athens' ancient Greek sites, and this little den didn't match either contemporary or current designs. His interest was piqued, and he discovered an unusual chapter in this historic monument's story...

Cooper believes that the added dwelling was, in fact, home to a devout follower known as a stylite or pillar saint. Part of an extreme and forgotten faction of the Christian faith, they believed living in high places brought them closer to God.

Seen in this image, also from 1860, the stylite would have been isolated in his sky cell and would have used ropes and baskets to obtain supplies from below. There you are, mystery solved!

Visitors to Venice frequently marvel at the watery avenues and canals and wonder how huge structures like St Mark's Basilica were built on water.

The origins of the city of Venice stretch back to the 5th century when the mainland inhabitants escaped the threat of Atilla the Hun and other foreign invaders by heading to the lagoon islands for safety.

Aside from early primitive dwellings, the significant stone structures were built around 1,200 years ago, and the oldest surviving buildings are said to be around 800 years old. So how did they do it?

Well, the answer is in extraordinary engineering. Long wooden piles were driven by hand and hammer through the soft mud and silt into the harder clay bed below, called ‘caranto’. Made from water-repellent trees such as oak or pine, they were staked close together with mud packed into the gaps for extra stability.

Wooden planks were then laid on top, followed by smaller bricks and stones, until a large slab of Istrian stone or marble could be put into place on the waterline. These stakes have survived for centuries and are still remarkably preserved, perhaps due to the low oxygen content of the water.

If you've ever been to the Canadian province of Newfoundland and Labrador, then you might have spotted a number of homes with seemingly random doors.

A common sight in Newfoundland, they have been the subject of questions for decades. But where did they come from and what is their purpose? Well, sadly, there’s no exact answer, but there are plenty of theories. Cheekily nicknamed Mother-in-Law Doors, many locals say that they are for ushering out unwanted guests!

Some believe the doors were added in 1949, when Newfoundland officially joined Canada. Fire regulations demanded that buildings have two exits. Since the regulations didn’t specify rules for these second doors, people created one wherever they liked.

It’s also thought that leaving off a staircase allows a building to technically remain “unfinished”, which would allow for some sort of tax break. Perhaps the most likely theory, however, is that in this part of Canada, snow can pile up and completely block ground-level doors. So, having a higher access point would be the perfect solution.

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