How eerie must it be to swim past submerged lamp posts, barbed wire and other remnants of an old Soviet prison while scuba diving in a former quarry? The setting is dangerous; visitors might brush up against sharp objects, and some have even died in diving accidents, but for avid explorers of abandoned places, the risks may seem worthwhile. After all, it’s hauntingly beautiful: the ruins of an old stone and concrete structure surrounded by turquoise waters, its underwater surfaces covered in algae and shellfish.

The ruins of this abandoned prison camp founded in 1938 are located in the small Estonian town of Rummu, within a limestone quarry where the inmates were once forced to labor. Its past is rather grim, as you might expect. The prison was well known for human rights violations, with frequent inmate deaths and hunger strikes demanding better treatment. Estonia regained its independence in 1991, and soon work at the quarry stopped. It quickly filled up with water, flooding any structures nearby. Other buildings that were part of the prison stayed dry and remained open as recently as 2012.

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Visitors often have to cut through fencing topped with barbed wire to gain access. It’s a popular spot for swimmers and divers alike, both local and those visiting from other countries. A Finnish group of urban explorers calling themselves Abandoned Nordic documented their dive at this ‘prison beneath the surface’ with stunning results, and wrote about the experience on their website.

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“We circled the largest building underwater, some sections of this particular building were above the waterline. The visibility in the water was fair but rays of midday sunlight revealed the walls and the shapes of the buildings in front of us. We swam inside from a large doorway inside the basement of a building with a partially collapsed roof. Some of the rooms were completely underwater. The rooms were full of concrete and darkness. Bars are still intact in the windows. Even though the buildings are grey, the penetrating greenness of the water brought warmth to the scenery. Nature has taken over this world a long time ago.”

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“The buildings rising from the green water form a bizarre sight. On a clear day, one can see the underwater structures, buildings and walls, easily from the sand hill next to the quarry lake. I’m not surprised why this place fascinates so many, including Tanja. Unfortunately, not much history remains from this odd place. Just like in Skrunda, documents of old photos are really hard to come by. I have never seen one photo from the active days of the Rummu prison camp. It seems like Rummu was born underwater, but still we can figure out that the place used to be very different.”

Read the whole account and see more photos at Abandoned Nordic.

Useless, defunct and more than a little surreal, ‘thomassons’ are the remnants of architecture and infrastructure left behind during demolition to leave behind a ghostly imprint of the past. These architectural relics are like scars: evidence of damage that never fully healed. Some passersby never even notice the stairs that end in a brick wall, the outlines of buildings that no longer exist, the doors that open to the air many stories above ground level. But for others, they have a sort of melancholy romance as a physical, tangible connection to bygone eras in a rapidly changing world, even if that ‘bygone era’ was just a few years ago.

Spotting these anomalies can feel like the discovery of hidden portals, as if you could stand in front of them and magically transport yourself right out of the space-time continuum if you just had the password or the secret handshake. For others, they’re like glitches in the matrix, just out of place enough to give you a momentary sensation of your surroundings being not quite real. An intrusion of the digital world into the physical.

So maybe it’s not surprising that communities have developed around finding, documenting and appreciating these urban oddities. The word ‘thomasson,’ if you’re not aware, was coined by Japanese artist Akasegawa Genpei in the ’80s, referencing a basketball player with a useless position on his team. He was a bit of a pioneer in the world of thomasson-spotting, archiving the vestigial objects he found around Japan in a magazine column, and then a 1985 book titled Chogeijutsu Tomason.

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The book was published in the United States in 2009, bringing the phenomenon stateside. But search for ‘thomasson’ on Instagram, Flickr, tumblr, Facebook and other social media platforms and you’ll see that, for whatever reason, this hobby remains most popular in Japan.

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Akasegawa referred to thomassons as ‘hyper-art,’ explaining that they may not have been created with artistic expression in mind, but nevertheless, they’re more artistic than intentional art itself. Indeed, they have more than a little in common with Dadaism, the early 20th century avant-garde art movement that “rejected the logic, reason, and aestheticism of modern capitalist society, instead expressing nonsense, irrationality, and anti-bourgeois protest.”

Would the construction workers who are ordered to tear down or alter part of a structure without erasing all evidence that it ever existed think of themselves as artists? Probably not, but it doesn’t mean they aren’t. When they become self-aware, does the whole movement threaten to become a mockery of itself? Hard to say, though it’s kind of fun to imagine. The idea of cities becoming more maze-like than ever, full of intentional dead ends, is either frustrating or delightful, depending on your particular perspective. You’d have new and creative excuses for being late to work.

For Akesegawa, a true thomasson meets two criteria: it must be totally and completely useless, and also regularly maintained, which adds another layer of absurdity to the object’s continued existence. That means ruins and abandonments don’t really count. The objects must be folded into a newer incarnation of their surroundings as if nobody could be bothered to remove them altogether, and possibly cleaned or repaired on a regular basis. Demolish that section of spiraling stairs that lead to the sky? Nonsense! Put a fence around it instead!

In our era of rapid urbanization and development, it’s easy to see why thomassons are so intriguing. Cities change so quickly, it can seem like the realities we’ve lived in during our own lifetimes have already been lost, despite how little time has actually passed. And who doesn’t dream of reconnecting with those old familiar environments, whose memories may already be fading in our minds?

Manually chipping away at rock for hours, two cave explorers have discovered a massive, previously unknown system of prehistoric caves beneath the streets of Montreal. Estimated to be around 15,000 years old, the Ice Age cave network was found about 30 feet beneath the city’s Pie-XII Park adjacent to the St. Léonard cave already popular with residents and visitors. These shafts tunnel almost 700 feet into the earth – most of their depths filled with water, and thus, pretty hard to fully explore.

Cavers Daniel Caron and Luc Le Blanc say they’ve suspected the existence of these caves since 2014, and spent much of 2017 exploring St. Léonard, which is already mapped, to find potential openings. They came across a narrow opening in the rock face that looked promising, but it was too small to enter, so they stuck a camera inside and took some photos of the chamber on the other side.

The cave explorers used hammers and cordless drills to break the wall down and get inside, finding a cavern with impressively high ceilings that leads to an underground lake. According to the Quebec Speleogical Society, Montreal was built right over this entire system without anyone ever realizing it was there, and Caron and Le Blanc may be the first humans ever to enter the newly-discovered areas.

Many cities all over the world are built right atop underground wonders, from quarries and catacombs to bunkers and smuggling tunnels, but the foundations of many others remain a mystery. Many of us likely walk over secret worlds every day without ever realizing it.

By now, most of us are aware of the abandoned, once-forgotten subway stations and other underground wonders hidden beneath the streets of cities around the world. There are even entire cities beneath cities, like Seattle’s Underground. But what about the more obscure secret spaces right under our noses, that we may pass every day as we go along our routines, never knowing of their existence? You could be walking over a reproduction of the Holy Land, a beautiful Art Deco time capsule, a secret canal or a (literally) underground drag racing strip without having a single clue.

Secret Entrance to the White House

(images via Elliot Carter, Atlas Obscura)

Residents of Washington. D.C. probably walk or drive past this unremarkable alleyway all the time, never paying particular attention to the vehicles that go in or come out. But it’s actually a secret back door to the White House created in the 1940s, and the only reason we know that is through archival newspaper reports from the time, when it was just a matter of relatively yawn-worthy public interest. Perhaps the Secret Service would rather we didn’t know about it, especially since they have installed a bulletproof kiosk into the wall at the entrance for their own staff. The secret route winds around the block, into an IRS building and ultimately empties into a subterranean granite vault built during World War II. No doubt, it’s just one of several such routes, and though it’s low-key public information, you probably don’t want to march right up to the H Street entrance unless you’re looking to get some special Secret Service attention.

Lower-Lower Wacker Drive Under Chicago

(images via: Chicago Reader, digiwonk)

Some people call it the Bat Cave. Others, the Magic Road. You need a special pass card to gain entrance at either end, which makes it feel exclusive to those who zip through its cramped quarters full of concrete pillars. Lower Wacker Drive, which first opened in 1926, is unknown to many Chicagoans, while those who’ve been aware of it for decades roll their eyes at every person who thinks they ‘discovered’ the ‘secret’ passage designed for service vehicles and convention buses. Many skyscrapers along the route open directly to Lower Wacker Drive at basement level for deliveries and garbage trucks. But many a proudly in-the-know Chicago resident may still be unaware that there’s actually a Lower Lower Wacker Drive, built in 1975 for parking and storage. Most people only find out about it when their vehicle is towed to a notoriously hard to access impound lot located on this level. Others who live in the skyscrapers nearby may just wonder if they’re losing their minds when they hear the echoes of the illegal drag racing that goes on along this subterranean route every weekend.

Chattanooga’s Secret Underground City

(images via: picnooga)

There’s a whole other Chattanooga under the current Chattanooga, and nobody knows why. When you descend into the basement levels of many old businesses built in the 19th century, you’ll find windows and doors that lead nowhere, evidence of a lower level that disappeared underground when the city built up its roads between 1875 and 1905. Some people think they did this to avoid flooding from the Tennessee River, while others believe they may have thought it would help stop the spread of infectious diseases like cholera that ravaged residents at the time. It’s hard to really get a sense of the size and scale of this forgotten layer, because it’s almost entirely located on private property. Documentation of construction at the time is almost non-existent, so there’s no digging through archives to solve the mystery. Historians don’t even know where the city got the soil to fill it all in. Naturally, the owners of some of these structures have turned them into tourist attractions with various kinds of tours, and legends of ghosts have proliferated.

A Hidden Stream Beneath Indianapolis

When it’s mentioned in the novel Underground Airlines by Ben Winters, the subterranean river called Pogue’s Run under Indianapolis seems fictional like everything else in the story, which imagines a reality in which slavery in America was never officially abolished. But it’s actually real, running under the city for two and a half miles, a popular destination for urban explorers, who often traverse it by bike. It’s dark and dank, infested with terrifyingly robust rats and gigantic insects. It was directed under the city back when urban streams were essentially open sewers, and mostly hidden under structures like an old parking lot that was removed in the ‘90s, revealing a stretch of it to the public. It lies beneath the only stretch of the city that isn’t perfectly gridded and symmetrical, its own proportions screwing up the plan, and ends where the canal converges with the White River.

Catacombs of Washington

(images via: Mr.TinDC, Lawrence OP, David, Flickr CC)

Of all the many secrets that can be found beneath street level in our nation’s capital, this complex of dim passages might be one of the strangest and most unexpected. Guests who want to explore it enter through a dramatic ‘secret’ gated entrance located near the pulpit of a Franciscan monastery. What they’ll find inside is an almost Disney-like recreation of ‘The Holy Land,’ full of fake graves and reproduction grottoes cast from aggregate cement. The Catacombs of D.C. were created by the monks for North Americans who can’t afford to take a trip overseas. For all the fakery, there’s one grave that’s actually real, containing the skeleton of a seven- or eight-year-old child believed to be a martyr from the second century.

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Secret Spaces 12 Architectural Easter Eggs Hidden Under Our Noses

If you’re afraid of heights, a mere glance at these photos taken by Russian daredevil photographer Angela Nikolau might be enough to give you the heebie-jeebies. The 23-year-old scales some of the tallest skyscrapers in Russia and Asia, either using a selfie stick, a drone, or bringing her boyfriend Ivan Kuzenetsov along to take the photos. And as if perching on the edges of structures at such extreme heights isn’t enough, she often does yoga poses or wears stilettos while doing so.

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The self-taught climber is not too concerned about bypassing security and breaking trespassing laws to capture these incredible images, and virtually no building is too tall. Angela and Ivan climbed all 2,000 feet of the Golden Finance 117 building in Tianjin, China last fall.

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Other illegal conquests include the Sagrada Familia in Barcelona, the Shanghai Tower in China, the Tsing Ma bridge in Hong Kong and the Eiffel Tower in Paris. Unsurprisingly, many of the photos have to be taken late at night to avoid being caught.

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Angela’s casual poses might be the most disconcerting aspect of the photos, especially for those of us who imagine death-gripping the edge if we managed to make it up that high. She’s often lounging dangerously close to certain death, holding on to a ladder with just one hand or hanging barefoot off cranes. In some images, she’s held aloft by her boyfriend, dangling hundreds of feet off the ground.

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Check out all of Angela’s images at her Instagram, @angela_nikolau.