This is the stuff that spy movies are made of. Belonging to the United Kingdom, the letters of last resort are exclusively written by the newly appointed prime minister. Four different letters are penned, which are then given to four submarines equipped with destructive Trident missiles. Within the letters are instructions telling the commanding officers what to do in the event of a nuclear strike on Britain. No one but the prime minister knows the exact contents of the letters, as they are kept sealed until nuclear war breaks out. In the event that nuclear war doesn’t break out (which, thankfully, it hasn’t), the letters are destroyed upon the inauguration of a new PM.

It’s hard to imagine a simple napkin being the subject of a state secret, but such is the magic of the imperial napkin fold. The napkins at Austrian governmental events are given the fancy fold, which results in a gorgeous flourish befitting the rich dignitaries who attend these types of events. Also known as the Hapsburg napkin fold, the technique is a guarded state secret, and it’s said that only two people at a time know how to do it; they then pass the knowledge on to another high-ranking official upon their deaths. Napkins folded in this manner are even kept in Austrian museums, public interest in their extravagance being so profound.

Coca-Cola has been around since 1886, and try as desperately as they might, no one has been able to replicate its distinct taste. That’s how you know you have a good beverage on your hands! Inventor John S. Pemberton kept his recipe a secret and even refused to write it down for fear of people copying his success; it was finally jotted down when Ernest Woodruff purchased the company in 1919. The physical recipe then made the rounds between New York’s Guaranty Bank, Atlanta’s Trust Company Bank, and finally the World of Coca-Cola, which is where it resides today. It is currently housed in the so-called Vault of the Secret Formula, and it remains a very closely guarded trade secret.

While HIV is largely linked to the 1980s, it continues to be a problem. In 2020 alone, it was estimated that nearly 40 million people were living with the disease. But regardless of its prevalence and very public history, there is still a lot about the retrovirus we don’t know. For example, humanity is still mostly unsure of where it came from. The leading theory is that African hunters in the early 20th century killed and ate chimpanzees infected with SIV – the S standing for “simian” – which then mutated into HIV in the human body. However, this information is typically populated with words like “probably” and “likely,” indicating that the origins of HIV are not definitively known, even to this day.

“Farmers’ Almanac” has been annually published since 1818, so it’s obviously doing something right. The “Almanac” makes long-term weather predictions in North America, and various scientific studies have proven a roughly 50% rate of accuracy. Not bad, considering the predictions come up to two years in advance and it seems like the local weather station doesn’t even know if it’ll rain tomorrow. Weirdly, almost nothing is known about the making of the “Almanac.” The forecaster is kept secret, and the “Almanac” itself has never revealed how it makes its predictions. The formula is reportedly kept inside an impenetrable box, and the world is left wondering just how in the heck these gods can so accurately predict the weather.

Living from the mid 12th century to the early 13th, Genghis Khan is the infamous instigator of the Mongol Empire, which was the largest connective empire in history. After taking over much of the known world, Khan died under unknown circumstances and was returned to his home country of Mongolia. Legend has it that the funeral procession killed anyone who witnessed it in order to keep his final resting place a secret. If that’s true, then it certainly worked, because no one today has any idea of where Genghis Khan is buried. Modern scholars believe that his tomb is somewhere around the Burkhan Khaldun mountain, but research in the area is difficult owing to restrictions imposed by the Mongolian government.

Many scholars and historians agree that Jesus Christ was a real person and that he was born sometime around 4 BC. However, a large chunk of his historical life remains unaccounted for, as no one knows what he was doing between the ages of twelve and twenty-nine. These are referred to by a variety of names, including his “silent years.” Of course, there are many theories. Some believe he was in Britain, others India. But the leading theory is that he was in Galilee, a region of both Israel and Lebanon, working as a carpenter under the tutelage of his father, Joseph. Following Jesus’s unknown excursions, he was baptized in Al-Maghtas around 28 AD, and it is here that his world-changing ministry began.

There’s something about submarines and secrecy. The United States owns various missile submarines that are guided by nuclear power, including the USS Ohio, Michigan, Florida, and Georgia. These are known as SSGNs. The missiles on board these subs have the potential to cause great destruction, but their whereabouts and activities are generally unknown. However, they literally surface from time to time. For example, Michigan appeared in South Korea in 2017, and Florida took part in Operation Odyssey Dawn in Libya. On June 28, 2010, a rare event occurred which saw three of four surfacing at once in response to Chinese missile tests. These four subs have been SSGNs since the 2000s, but most of their actions and locations have remained a secret.

It’s amazing how little we know about a UNESCO World Heritage Site. Found in China’s Shaanxi (shan-SHEE) province is this world-renowned mausoleum, which is most famous for its Terracotta Army. Constructed from 246 to 208 BC, the area houses approximately 8,000 terracotta soldiers and the tomb of Qin Shi Huang (chin sheux/sure h’wong). This is a massive underground necropolis containing…well, no one really knows. The burial tomb itself still hasn’t been excavated, but Han dynasty historian Sima Qian states that it contains “fine vessels, precious stones, and rarities.” But, like many archeological discoveries, it has probably been long looted. Perhaps we’ll never know what it truly looks like within the mausoleum complex.

When it comes to highly classified areas, it doesn’t get more famous than Area 51. Found in the Nevada desert, Area 51 is a top-secret military facility with ties to cutting edge technology. The place is so secretive that it wasn’t officially unveiled by the CIA until 2013, even though it was very obvious that something was in the desert. Area 51 is officially known as a military training facility and supposedly a testing ground for both experimental aircraft and high tech weaponry. Owing to its secretive nature, both trespassing and flying over the site are grossly prohibited and dangerously enforced. Naturally, this has given rise to a swath of conspiracy theories. Are aliens inside Area 51? Perhaps we’ll never know.