1. The Dyatlov Pass incident commons.wikimedia.org Nine dead hikers, a truckload of unanswered questions, a government cover-up, and even some conspiracy theories involving UFOs. This incident wouldn't look out of place on an episode of The X-Files. Oh, and there's a theory involving yetis, because why not at this point? 2. The Kentucky meat shower Thinkstock / BuzzFeed This one is pretty much exactly as it sounds. On a spring day in 1876, the skies opened up over an area of Bath County, Kentucky, and down poured pieces of meat. According to two guys who ate the meat – because who wouldn't want to eat mysterious flesh that's fallen from the heavens? – it tasted of mutton. Nice. 3. The Man in the Iron Mask commons.wikimedia.org You've probably heard of this story through its countless retelling in film and literature, but the historical truth is even stranger than any twist Hollywood could put on the tale. Over three centuries later and people are still trying to figure out the identity of the man mysteriously imprisoned and forced to wear a mask to hide his identity. 4. The Hinterkaifeck murders en.wikipedia.org This case contains all the hallmarks of a horror movie: a creepy house in the country, complaints of a haunting, the sound of footsteps in the attic, and finally a whole family being slaughtered by an unidentified killer. You'll definitely want to check that your doors aren't unlocked after reading this. 5. The Original Night Stalker en.wikipedia.org The Original Night Stalker, also known as the Golden State Killer and the East Area Rapist, terrorised California's Sacramento County for a decade – burgling more than 120 homes, raping 45 people, and killing 12. He was known to call victims beforehand, and in some cases phoned them afterwards, taunting them. The perpetrator of these crimes is believed to still be alive, and the FBI recently launched a media campaign in the hopes of finding the man who's eluded law enforcement for so long. 6. The Hum Flickr: tessawatson / Creative Commons You don't appreciate silence until it's gone, and that's especially true for people who claim to have been plagued by this unidentified sound. The Hum is a constant, low-pitched noise that's been heard at various locations worldwide, from the UK to New Zealand. 7. The Mary Celeste commons.wikimedia.org The Mary Celeste is one of the most famous examples of a ghost ship – a ship found with its entire crew missing under mysterious circumstances. The vessel was discovered abandoned, but in reasonable order, off the coast of Portugal, leading to lots of speculation about what happened to the missing crew. 8. D.B. Cooper Associated Press In 1971 an unassuming man in a black suit and tie boarded a commercial airplane heading for Seattle, Washington. Mid-flight, the calm and polite passenger handed a note to the nearest flight attendant claiming that he was in possession of a bomb and was demanding $200,000 and four parachutes. Upon landing, the hijacker got what he wanted, and his next instructions were for the plane to head for Mexico City. At some point during the journey Cooper made use of his parachutes and jumped from the plane with his $200,000 ransom, never to be seen again. 9. The Wow! signal commons.wikimedia.org The Wow! signal gets its name from the signal's discoverer, astronomer Jerry R Ehman, wrote the "wow!" on the side of the printout containing it. So what got an astronomer excited enough to use an exclamation mark? The answer is an unexplainable radio signal that may point towards the existence of extraterrestrial beings. Despite many attempts, the signal has never been found again. 10. Tarrare Hulton Archive / Getty Images Tarrare was an 18th-century Frenchman renowned for his bizarre eating habits and insatiable appetite. During his career as a showman he was known to eat stones, live animals, and whole baskets of apples – while never to managing satisfy his hunger. Despite his diet, he remained of average weight. 11. The Max Headroom broadcast signal intrusion youtube.com Seriously, this video will spook you out. A Reddit user claims to know those involved. On 22 November 1987, during an episode of Doctor Who, a Chicago television station had its broadcast hijacked. What followed was a creepy video involving an unidentified man in a Max Headroom mask. Here's a video of the incident itself. 12. June and Jennifer Gibbons John Firth / Getty Images There's something inherently creepy about twins, and even by twin standards of creepiness, these two are really ~creepy~. Born in Wales during the '60s, June and Jennifer cut off communication with others and only spoke to each other, even speaking in a way that was unintelligible to everyone else. The story only got more bizarre as the twins grew up and were eventually admitted to Broadmoor psychiatric hospital. 13. The Tunguska event commons.wikimedia.org On 30 June, 1908, a large explosion occurred over an isolated area of Russia – the nearest town was over 35 miles away but still felt the effects, which included windows smashing. The blast produced 85 times more energy than the atomic bomb dropped on Hiroshima and flattened an estimated 80 million trees. Although the destruction is widely believed to be the result of an asteroid, no impact crater has been found, leaving the incident open to alternative theories. 14. Cicada 3301 en.wikipedia.org Every year since 2012 a secret organisation has been puzzling the internet by anonymously posting complex puzzles online. Is this a recruitment tactic by the CIA or illegal hackers? Or maybe it's the work of something more sinister, like a cult. 15. The green children of Woolpit en.wikipedia.org A real-life fairy tale. In the 12th century, a sleepy village in Suffolk, in the UK, was visited by two green-skinned children. They were alleged to speak in a strange language and claimed to have come from an underground world filled with other green people. Weird. 16. The Voynich manuscript commons.wikimedia.org The Voynich manuscript is a handwritten book in an unidentified language and filled with diagrams and drawings, from sometime in the 15th century. Codebreakers have attempted to decipher the meaning of the strange book for centuries, but with no luck. 17. The Tamam Shud case commons.wikimedia.org The Tamam Shud case involves the discovery of a man found dead on an Australian beach. From there the case went down a strange path, involving a book of 12th-century poems, an encrypted message, and possible international espionage.