Humans aren't meant for the ocean, but something about its mysterious deep dark depths is equal parts bone-chilling and captivating. There is a reason sailors continue to cross it, and billionaires trap themselves in fancy DIY submarines to visit its deepest treasures; even though the ocean makes up most of our planet, we know less about its floor than we do the surface of Mars. 

For example, it's highly doubtful that there is an actual "lost city of Atlantis," but the concept of ancient underwater cities isn't entirely mythological. After the ice age, many prehistoric groups found their settlements underwater, and there have been many recent discoveries of Stone Age ruins underneath shallower waters. 

"The bloop" is another massive ocean mystery, involving one of the loudest sounds ever recorded. The sound was registered by underwater sensors thousands of miles apart around the globe, and there is no unifying theory to its source. Occurring in a remote South Pacific region, some scientists think it can be attributed to cracking ice, but who knows? 

The ocean is big and terrifying, but we can't get enough of it. Here are 23 disturbing facts to float your boat.