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.) Flickr / Dimitris Agelakis 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.

Medical Symbol (Wikimedia) The universal medical symbol is a snake coiled around the Rod of Aesclepius, the Greco-Roman god of medicine. According to legend, Aesclepius, the man-god son of Apollo, learned to heal from both his deific father and his wise mentor, the Centaur Chiron. The Rod of Aesclepius has passed down to us as a paragon of the healing arts from ancient stories of this mythological figure’s medicinal exploits.

What is the hardest mountain to climb? Is it the tallest, the steepest, the one with the slipperiest rock walls or the fewest handholds? The one with the harshest weather? There are a lot of different factors that go into determining the difficulty of a climb. To a large degree, difficulty is a subjective measurement. But we can still come up with a list of challenging climbs based on a combination of these factors as well as the reports of climbers who have actually tackled these giants.

Few ideas get the blood flowing more than that of revolution. Revolution means change, and when change is desperately needed, a revolution can empower us to do more, be more, achieve more. Through revolution, we can overcome adversity and stagnation and rise up to fulfill our potential. And there’s nothing to incite a revolution like a revolutionary man or woman who takes a stand against the established order. Revolutions don’t just happen in politics or war.

Flickr / Andrew Mason Blood flows through a complex network of veins within our body, carrying nutrients to our organs, fighting off disease, and taking harmful materials to areas where they can be neutralized and disposed of. Blood is made up of 95% water, which allows it to flow easily between organs. Blood is made of a complex number of proteins and chemicals. Hemoglobin is the primary thing that gives blood its red color.

If you’re out in the wild, what’s the last creature you want to encounter? A shark? A rattlesnake? A jaguar? There are a lot of different traits which make animals dangerous. Some animals are particularly aggressive. Others are stronger or faster than we are, or have razor-sharp teeth. Still others are venomous, and can poison us with a sting or a bite. Others yet are clever and cunning. Here are the top 10 most dangerous animals in the world.

Diamonds, rubies, sapphires, and emeralds are all considered to be precious gemstones, whereas most other types of gemstones (quartz, tiger’s eye, agate, etc.) are filed under the semi-precious category. The reason that diamonds, rubies, sapphires, and emeralds are so prized is largely because they are rare, whereas most semi-precious gemstones are relatively common by comparison. The rarer a gemstone is, the more expensive it tends to be. What are the most valuable gems in the world according to both rarity and price?

Wikipedia/Ricardo Liberato The pyramids of ancient Egypt have rendered observers awestruck from the day the royal tombs first rose from the desert floor. Thousands of years ago, people were just as dumbfounded by their visual impact as we are today, and just as prone to mythologizing their origins. The astonishingly prescient achievement of the pyramids has fueled speculation the geometrical structures must have been made by an alien species or perhaps a race of giants.

All of us have been on roads at one time or another that scared us. Maybe it was the steep drop-off along the road side, or perhaps it was all those signs warning you that a rockslide was possible at any moment. Perhaps it was a lot of sharp twists and turns, low visibility, a steep grade, or bad weather. Maybe it was just the other drivers who scared you. But it probably got you to wonder—were you driving on one of the world’s most dangerous roads?

Heading into 2013, the list of the 10 most dangerous cities in the US per capita didn’t include many of America’s largest cities. The most dangerous major American cities were Atlanta (26th), Baltimore (27th), Washington, DC (46th), Philadelphia (50th), Newark (51th), while New York City didn’t even make the top 100 most dangerous list. Instead, the 10 top most dangerous American cities were the decaying manufacturing hubs and relatively smaller cities with histories of racial tension and poverty.