About 75 miles north of San Francisco lies a 2,700-acre campground tucked in among the firs and redwoods of northern California. At the campground’s center is a lake, which was made by artificial means. Over the lake is what’s known as the “Owl Shrine” — a huge wooden owl overlooking a tiered, outdoor stage.

But unless you’re rich, powerful, and male, you’ll probably never set eyes on the camp, or see the “Cremation of Care” ceremony performed before the Owl Shrine each year, or witness whatever shenanigans the members of the camp’s secretive group get up to for the two weeks during the summer they’re in residence there every year. Bohemian Grove, you see, isn’t for the likes of us mere mortals, and the Bohemian Club admits new members only rarely, by invitation, and at great cost (we’re talking a $25,000 initiation fee).

Although the rules of Bohemian Grove are meant to prohibit business dealings and shop talk while you’re there, countless deals and decisions have been made among its members over the century and a half both the Grove and the Club have been around. Security, naturally, is tight — so tight that any hope you might have of trying to sneak in to see it should probably be put to rest before you even try.

You’re probably familiar with Camp David — the “famed rural retreat for presidents,” as Google Maps describes it, located in Catoctin Mountain Park in Hauvers, Maryland. But you might not know about the Raven Rock Mountain Complex, despite its proximity to Camp David — it’s just 12 miles away. Built between 1951 and 1953 (hi there, Cold War), it’s officially a U.S. military installation; what it mostly exists for, though, is as an “alternative seat of government,” should anything ever… happen that might require it.

Basically, it’s a bunker. A huge, massive bunker built literally inside a mountain for maximum security. It’s where the Department of Defense intended to go if the Pentagon were ever destroyed. It’s where Dick Cheney was evacuated to on 9/11. And although, as Atlas Obscura notes, “you’re perfectly within your rights to drive up to the barbed wire or take a picture from afar of the communications antenna,” that’s as close as you’ll ever get to the Raven Rock Mountain Complex.

Like many modern cities, Moscow has a subway system that helps millions of people get around the city every day. Unlike a lot of modern cities, however, Moscow also allegedly has an… alternative subway system. A secret one. One said to have been built during Stalin’s time in power and still operated by the Main Directorate of Special Programmes and the Ministry of Defense today.

Those who believe in it call it Metro-2, so as not to confuse it with the actual Moscow Metro. Supposedly longer than the regular Metro, Metro-2 is said to connect a number of notable locations throughout Moscow — the Kremlin, the Federal Security Service headquarters, the airport Vnukovo-2, and a subterranean town called Ramenki, among others. Groups of urban explorers who call themselves “diggers” have said they’ve located entrances to Metro-2 and explored it extensively — but the existence of the alleged system remains largely unconfirmed. The Russian government has never officially acknowledged it, and most officials will deny knowing anything about it if you ask them. Still, though — the rumors persist. It’s quite the story, after all.

Between the Italian cities of Venice and Lido, there’s an island that’s been abandoned for more than 50 years. Officially, it’s called Poveglia — but you might hear it spoken of from time to time as “the plague island.”

The first historical record of Poveglia dates back to 421, but although it was merely residential for many centuries, it became something else in the late 18th century: A place to quarantine people sick with the plague and other highly contagious illnesses. It later became a psychiatric hospital, but after the facility closed in 1968, the island was vacated and has remained as such ever since.

It went up for auction in 2014, but although one bid was accepted, the deal ultimately didn’t go through. A grassroots movement has been attempting to save and rehabilitate the island in recent years; however, this movement, too, has yet to see significant gains.

You can’t really land on Poveglia these days — due to the ruined structures and buildings still standing on the island, it’s not safe — but you can take a boat trip around it; a tour company in Venice called Classic Boats Venice has a tour on a beautifully constructed traditional Venetian boat that starts in Certosa, spends about a half hour passing around Lazzaretto Vecchio, and then circles Poveglia for an hour before returning you home.

Personally, I can’t think of Svalbard without thinking of the His Dark Materials series, but alas, there are no actual armored bears living on this Norwegian archipelago in real life. One of the things that is there, though, is of the utmost importance: The Svalbard Global Seed Vault. An impressive facility built into the side of a sandstone mountain, it acts as backup storage for the 1,700 genebanks scattered throughout the world that keep collections of food crops safe — that is, in the event that the global food supply is decimated and those other facilities fail, it’s our only means of survival. It is, as the seed vault’s website puts it, “the final backup.”

Opened in 2008 — and by “opened,” I mean that’s when the first seeds arrived for storage — the Svalbard Global Seed Vault currently contains nearly one million samples, although it’s capable of storing up to 4.5 million varieties of samples and 2.5 billion seeds. They’re sealed in three-ply foil packets, as well as heat sealed in order to keep out moisture. And the facility’s location is ideal for its purpose; the permafrost can keep the seeds frozen even if the power fails.

As is the case with many of the other locations on this list, you can take photos of the outside of the facility (as long as you don’t mind traveling to one of the northernmost points in the world) — but you won’t be getting inside anytime soon. Access is curtailed; the seed vault isn’t even regularly staffed. You can take a virtual tour here, though, if you’re curious about what our last ditch survival plan looks like.

Located in the Russian federal subject currently known as the Republic of Bashkortostan, Mezhgorye is what’s called a “closed town” — a secret military or research settlement that may or may not officially “exist.” Many of them aren’t marked on maps in any way, and those who live in them aren’t allowed to tell anyone outside the settlement where their place of residence is. Although they were considerably more common during the era of the Soviet Union, a number of closed towns still exist today (the Russian government has acknowledged about 40 of them) — and Mezhgorye is one of the most mysterious. Indeed, it’s sometimes referred to as “Russia’s Area 51.”

Although Mezhgorye was founded in 1979, it wasn’t given its current name or even considered a town until 1995. It’s not currently known what exactly goes on there, either, although rumors have been circulating for some time that it plays host to a nuclear missile base, several military battalions, and some kind of massive, underground base. According to the 2010 census, there were about 17,000 people living there — although it’s anyone’s guess if that figure is truthful.

But that’s not all that’s odd about this section of the Ural Mountains. Mezhgorye is also quite near Mount Yamantau, which the Russian government has stated is merely a mine—but which the U.S. government has long believed houses a complex not unlike the Cheyenne Mountain or the Raven Rock Mountain Complexes.

To the west of Cluj-Napoca, which ranks among Romania’s most populous cities, lies the Hoia Baciu forest. It’s not huge — only about three square kilometers — and it’s easy to visit; indeed, it’s a popular recreation spot, with bike trails, archery ranges, and paintball and airsoft arenas. But some who visit — and, in particular, those who visit an area in the forest known as the Clearing — report experiencing… unusual events while inside the confines of the dark sea of trees. Not for nothing do people refer to it as the creepiest forest in the world.

Widespread interest in Hoia Baciu didn’t actually pique until 1968 — but when it did, it was for good reason: That was the year a military technician named Emil Barnea claimed to have captured photographic evidence of a UFO in the Clearing. As the Independent noted in 2017, “What differentiates this story from other UFO claims is that Barnea had nothing to gain from reporting the sighting, and everything to lose. The Communist government equated a belief in the paranormal with madness and state-sabotage, and Barnea lost his job in a country which had no support for the sacked.”

But that photograph was just the beginning. Even today, commonly experienced phenomena include floating orbs of light, disembodied voices, and the occasional apparition. Unpleasant physical symptoms might strike you while inside the forest, as well — nausea, headaches, anxiety, or the feeling that you’re being watched, for example. Electronic devices might fail; additionally, any photographs taken might turn out to depict spectral figures not present at the time the shot was made.

And, of course, there are the stories — stories of people who vanished into the forest, and, when they emerged again years later, having no memory of where they had been for all that time. The forest is even rumored to have been named for a shepherd who disappeared from it along with 200 of his sheep one day.

With rooms starting at around $318 per night, the Greenbrier Resort in White Sulphur Springs, West Virginia is fancy. Tucked away in the foothills of the Blue Ridge Mountains, it features beautiful golf courses, a stunning spa, lots of shopping, a casino, and a variety of dining options.

It also has a bunker stock with supplies that was once intended to house Congress in the event of an emergency.

Built between 1959 and 1962 — concurrently, it should be noted, with the construction of a major addition to the hotel itself — Project Greek Island, as it was called, housed more than a thousand beds in a massive dormitory, each of which was assigned to a specific person for a full three decades. The facility also featured a kitchen, hospital, broadcast center, and several auditoriums — everything Congress would need to keep living and working if the unthinkable occurred. The walls of the bunker were two feet thick and made of reinforced concrete; they were capable of withstanding a nuclear blast. It closed with a vault door for maximum safety and security.

And for 30 years, no one except those on a need-to-know basis had any idea it was there.

A Washington Post exposé published in 1992 put an end to Project Greek Island; it was decommissioned after the paper’s investigation was made public. But even though it’s no longer used for its intended purpose (and, indeed, never was used for that purpose), it’s still there now — and, in fact, you can tour it. The Greenbrier’s 90-minute look at the place is priced at $39 for adults and $20 for kids between the ages of 10 and 18. Find out more here.

The city of Bielefeld in the northwest of Germany has a population of around 333,000. Founded in the 13th century BCE, it’s old and cute; formerly a major linen producer, it has within its bounds a number of historical sites, including Sparrenburg Castle.

Or at least, that’s what they want you to think. (Who “they” is remains to be seen.) Some believe that Bielefeld… doesn’t actually exist. That you can’t visit it, let alone live in it, because it’s not there. It’s a smokescreen for… something. No really knows what, although there are theories, of course. But those who believe there’s something more to the supposed “city” than at first appears refer to the whole situation by the most nefarious of names: The Bielefeld conspiracy.

The litmus test for whether someone is part of the conspiracy is this series of questions: Do you know anyone from Bielefeld? Have you ever been to Bielefeld? And lastly, have you ever met anyone who has been to Bielefeld? If the answer to all three questions is no, congratulations! That person is not part of the conspiracy. If answer to one or more of the questions is yes, though, it’s recommended that you back away from that person. Back away slowly and calmly… but back away.

The Bielefeld conspiracy just an urban legend, of course; Bielefeld does, in fact, exist, and you can, in fact, visit it. The legend started as a joke on Germany’s Usenet in 1994, and in the intervening decades, it’s taken on a life of its own. Angela Merkel even referenced it at one point.

No doubt you’re already familiar with the Parisian catacombs; the massive, centuries-old ossuary is one of the French city’s most notable pieces of history, as well as one of its most intriguing tourist attractions. But the section of the catacombs that’s actually open to the public is just a tiny part of the complete system — a system which is so vast, people can very easily get lost in them… and never be found again.

Some of these disappearances are fact — and sometimes, they have happy endings: In 2017, for example, two teenagers spent three days wandering the pitch black labyrinth of bones before being located and rescued. Some of the disappearances might be tall tales, though; for example, rumors that video footage from the ‘90s show a man’s final moments in the catacombs before he sprinted off into the darkness, never to be seen again, have never been confirmed as true. Either way, though, what is true is that the catacombs are 150 miles long, that there is no light down there, and that the many, many difference entrances to them scattered throughout Paris are sealed up for safety reasons almost as soon as they’re found.

Some people do manage to sneak down into the portions that are technically off-limits; they’re called cataphiles, and sometimes they do things like hold clandestine film festivals down there.

But they’re not supposed to be there. No one is. No one but the dead, at any rate.

One of New York’s creepiest secrets is hiding right in plain sight — just off the coast of the Bronx, in fact. One of a pair of small islands, North Brother Island was uninhabited until 1885, when Riverside Hospital moved there from its previous location on what’s now Roosevelt Island. Initially specializing in smallpox, the hospital later expanded to a wide variety of illnesses — typically those which required quarantining at the time. “Typhoid Mary” Mallon — the first asymptomatic carrier of typhoid fever identified in the United States — was quarantined at Riverside for a total of almost 30 years between 1907 and her death from pneumonia in 1938.

Riverside Hospital closed not too long after that, leading to the island playing host to a number of other facilities in the following decades, including veteran housing following the Second World War and a rehabilitation and treatment center for teens. The rehabilitation center was closed in the 1960s due to allegations of staff corruption and patient abuse, however, and ever since then, the island has been vacant, its existing buildings slowly eroding as the years wear on.

North Brother Island does, however, serve a purpose these days: It’s a bird sanctuary with a large heron population. Visits are only rarely granted, and only if you have a really, really good reason for going there — but if you want to inquire about it, you can do so by contacting the New York City Department of Parks and Recreation.

The catacombs aren’t the only forbidden secret hiding beneath Paris’ streets; there’s also a 1,290-square-foot bunker lurking underneath Gare de l’Est railway station in the 10th arrondisement. Originally designed to be an air raid shelter for use in the Second World War, the bunker was only half-built when France fell to German occupation; it was finished by Germany, and although we don’t totally know what it was used for, it includes a telephone exchange and a machinery room, among others.

Here’s the weird thing: According to Atlas Obscura, it’s impeccably maintained by the French railway network, SNFC. Why? Who knows. But they’re definitely doing the upkeep — and even preserving it as it was during the war.

It’s not accessible to the public, but the next time you’re at the station, look for a trapdoor on one of the platforms in the station. Know that, when opened up, that trapdoor reveals a staircase. And know that at the bottom of that staircase is the entrance to the bunker.

Universally acknowledged as one of the weirdest airports in the world, the Denver International Airport lies at the center of a surprising amount of conspiracy theories. First, there’s the puzzle of its dedication capstone: Featuring the symbol of the Masonic lodge and bearing the legend of a mysterious entity called the “New World Airport Commission,” it’s led many to believe that the airport is somehow involved in the New World Order conspiracy theory. Then there are the extremely bizarre murals located on Level 5 of the Jeppesen Terminal, which some think further supports the idea of a possible New World Order connection. It’s also rumored that there’s a network of underground tunnels or bunkers beneath the airport, although to what end, no one knows.

And then there’s the freaky horse statue outside the airport, which is officially titled “Blue Mustang,” but colloquially referred to as “Blucifer” due to its color and demonic appearance: I kid you not, it actually killed its creator while he was sculpting it.

Like I said: Weird.

Obviously, the Denver International Airport isn’t off-limits to the public — it’s the largest airport in North America by size and serves nearly 65 million passengers each year. And the odd stuff is likely all just a wacky coincidence… but it still kind of makes you wonder what the heck is going on with the place, doesn’t it?

You might recognize Hashima Island if you see pictures of it; also known as Battleship Island due to its shape, it’s been used as either location inspiration or an actual shooting location in a variety of major films, including the 2012 James Bond flick Skyfall and 2015’s live-action version of Attack on Titan. Like Poveglia and North Brother Island, it has the kind of appeal that only an isolated location left to decay on its own has — it’s equal parts terrifying and, strangely, beautiful.

In the 1880s, Hashima Island was a coal mining outfit. Originally, workers were ferried in daily from Nagasaki; later on, though, housing was built for workers and their families directly on the island itself. Its peak population was over 5,000 — but after the coal began to run out in the 1970s, the island was quickly abandoned. It’s remained as such ever since, everything on it just left to rot.

But that’s not the full story, either. During the Second World War, it ran on forced labor from prisoners of war (mostly from Korea and China), with an estimated 1,000 workers dying due to the harsh conditions to which they were subject.

Unlike Poveglia and North Brother Island, Hashima Island, which was named a UNESCO World Heritage site in 2015, is open to tours; however, it’s, uh, not in great shape, so if you book a tour, you do so at your own risk. Efforts are being made to preserve the island, but it’s slow going, according to National Geographic.

For more info on how to book a tour, head here.

Although there’s a lot we still don’t know about Area 51, we do at least know that it exists now; the government officially acknowledged it in 2013. But what Area 52? Does that exist? And if so… what the heck goes on there?

If you do some digging, there are a couple of different sites and installations that might be referred as “Area 52.” One of them is the Tonopah Test Range — an installation located about 70 miles north of Area 51 which, as its name might suggest, is generally used to test various weapons technology. The other is Dugway, a proving ground located in Utah. Both, naturally, are top secret, with access being heavily restricted.

Neither one of them has ever been confirmed to be Area 52. The existence of an Area 52 more broadly hasn’t been confirmed, either.

But that’s not stopping people from wondering about it...