History is full of mysteries, partly because the people that gave rise to them failed to account for the insatiable curiosity of future mystery-mongers by leaving adequate evidence behind. Fair enough, but that shouldn’t stop us from mystery-mongering and treasure-hunting to our hearts' content. For all the Robert Stack-inspired sleuths in the audience, here are your top 10 unsolved historical mysteries.

10. Phaistos Disc (c. 1700 B.C.)

A second-millenium artifact covered in hieroglyphics no one can read, the Phaistos Disc contains a magical curse, a geometric proof, a militant call to arms — or perhaps the meaning of the cosmos as understood by the ancient Minoans. It really depends on who you ask. The Phaistos Disc is tantalizingly descriptive of who-knows-what, its characters inscribed on both sides in a spiralling pattern. The famously frustrating clay plate is the undeciphered Rosetta Stone of Europe’s earliest culture.

9. Voynich Manuscript (c. 1400 A.D.)

For years, people thought it was a hoax. The Voynich Manuscript seems like it could be a prop in a King Arthur tale, but there’s no author to tell us what it means. One of the great linguistic mysteries in history, the Manuscript is written in “Voynichese” — an unknown language. Carbon-dated to fifteenth-century Europe, it appears to be the only remaining artifact of its culture. Many scholars have spent their careers trying to crack its code, to no avail. Studying its murky text is considered a great way to commit academic suicide.

8. Hitler’s Gold (1945)

Adolf Hitler was one of the wealthiest men of the twentieth century. While in power, he amassed a vast fortune, much of it by illegitimate plunder. In 1945, the suicide of the Fuhrer triggered the overnight theft of more than $3 billion worth of his gold bullion, diamonds, priceless artworks and stolen currency. Quietly lifted from the vaults of the Reichsbank, it was the largest bank heist in history. Later, some fragments of the stolen booty turned up, but most of the Nazi hoard disappeared without a trace. We may never know who pocketed the spoils of Hitler’s wars.

7. GIs of the Vietnam War (post-1973)

The Vietnam War saw the death of more than 58,000 Americans, but more than 1,650 GIs neither died nor returned home, per Defense Department figures. Most were last seen in Vietnam. The so-called ‘POW/MIA’ movement has insisted missing American soldiers remained in captivity after 1973 as live prisoners-of-war under the Communist government. While the movement’s assertions have dominated the issue for years, the actual fates of the soldiers have yet to be resolved. Were they killed or tortured? Did they defect and set up shop in Asia? We may never know.

6. Jack The Ripper (1888)

One of history’s most infamous serial killers, Jack the Ripper is known to us only through his grisly moniker. The Ripper murdered at least five prostitutes in cold blood during the Autumn of Terror in 1880s London. After slitting his victims' throats, he disemboweled them in a curiously meticulous manner, after the fashion of someone with extensive medical knowledge. With his deeds loudly amplified by the popular press, the faceless killer evoked unprecedented horror and panic in the Victorian population. Today, Jack the Ripper’s true identity remains an exasperating mystery well over a century after his ghastly spree.

5. Easter Island (c. 1200 A.D.)

About 8oo years ago, a gang of Polynesians fled their home and sailed across the ocean until they ran aground three extinct volcanoes in the middle of the South Pacific. They had found Easter Island, one of the most remote places on earth. In the beginning, it was paradise. The people lived well and carved megalithic monuments called Moai in honor of their good fortune. But something went wrong.

By the time the Europeans arrived in the 1700s, the people had vanished. The island was stripped of all its vegetation. Once-fertile soils lay barren. Rat bones were everywhere. Moai lay unfinished, as though the carver was interrupted mid-chisel. What happened? The mysterious clues left behind suggest some kind of terrible apocalypse.

4. ‘The Bunker’ (September 11, 2001)

The terrorist attacks in New York City on September 11, 2001 are doused in gallons of mystery. Consider WTC-7. A lesser-known casualty of the attacks, the third WTC building that fell on 9/11 was a block north of the Twin Towers and housed the offices of the Secret Service and CIA. Known as “The Bunker,” WTC-7 wasn’t hit by a plane but, allegedly, succumbed to fire.

This official version of events would make the 47-story high-rise the first and only instance of a tall building collapsing due to fire. No other steel-framed skyscraper has ever burnt to the ground. Of course, there’s a first time for everything, but official accounts have failed to satisfy more than just conspiracy theorists, making WTC-7’s unlikely downfall one of the biggest mysteries of recent decades.

3. Malaysia Flight 370 (March 2014)

Too many unanswered questions — that’s what relatives of the passengers aboard Malaysia Airlines Flight 370 are saying about the plane that disappeared into thin air en route to Beijing in early March 2014. The Malaysian government has declared there are no survivors, but satellite analysts say “nothing is final." That’s because no wreckage or bodies have actually been found.

The official announcement of the passengers' demise was countered by angry demands for tangible proof. Whether Flight 370’s fate is settled or lingers on without resolution, the story of the plane lost at sea drives home the darker side of mysteries: they invariably deny closure to those who need it most — the people left behind to piece together what really happened.

2. Extinction of the Dinosaurs (66 MYA)

The extinction of the dinosaurs has been paleontology’s Great Mystery since the paleo-beasts' fossils were first uncovered. The evidence depicts a mass extinction event some 66 million years ago. What on earth happened? Was it climate change or acid rain? What about disease, or maybe dinosaur egg-munching mammals?

Today, the most popular explanation is the asteroid theory. According to the theory, it was the irradiating aftereffects of a jumbo comet that did the cold-blooded race of giants in. In 1991, the extraterrestrial smoking gun was found at the Yucatan Peninsula: a 130-mile-wide imprint dubbed the Chicxulub Crater. The impact of its comet would have blasted the energy equivalent of a billion atomic bombs. Now, the real mystery is: could it happen again?

1. End of the Universe (20 Billion Years From Now)

When did the universe begin? What happened beforehand? And more importantly, will it end? According to theoretical physicist Stephen Hawking, the universe is about 15 billion years old. Although it is often presumed eternal, the universe is actually both finite and dynamic, changing over time. Galaxies are moving away from each other, against the flow of gravity. This counterintuitive motion hints at an aboriginal explosion that set the contents of the current universe on their present trajectories: the ‘Big Bang.’

What preceded the Big Bang is an enigma. Was it another universe or nothing at all? Whatever existed before our own Bang isn’t known, because it cannot be measured. It’s a permanent mystery. As for the end of the universe, that, too, is unclear. Eventually, things could return to a singularity of infinite density and re-explode, creating a whole new universe. Even Stephen Hawking doesn’t know for sure. But if that occurs, no worries; it probably won’t happen for another 20 billion years.