Our brains are pretty good at physics. For instance, you can watch somebody kick a soccer ball in front of you, and you can run to the spot where you and that soccer ball will intersect, taking into consideration the speed of both you and the ball — so smart! Not only that, we can look at one object balancing on another and tell how sturdy it is without so much as touching it.
But sometimes our brains make uneducated mathematical guesses, and one of these is Kummakivi, the balancing rock in Ruokolahti, Finland. If it was up to your brain, Kummakivi — which means "strange rock" in Finnish — wouldn't exist. It's a boulder resting on a lump of rock in a position that, to our monkey engineer brains, appears impossible, or at least dicey. Extremely slap-dash and temporary work, at best. And yet Kummakivi sits quietly in its Scandinavian forest, racking up the centuries. Millennia, even.
Kummakivi is huge — about 23 feet (7 meters) long. It rests on the tiny, steeply pitched footprint of a smaller mound of rock that rises from the forest floor. The balancing boulder appears to be about to slide right off its perch, but it can't be moved — at least by human muscles. The reason for this isn't as mysterious as it might appear: Kummakivi is large, but large things aren't necessarily more likely to be affected by gravity than small ones. Kummakivi is very rough, which helps it stick in place, and it's not the same density throughout. The center of gravity looks off when you inspect the balancing rock with your eyes, but it's actually doing exactly what physics would have it do.
But the real question is, how did it get there?
People have probably always wondered that, but we'll never know because it has been there approximately 12,000 years — way before we started recording anything. However, Finnish folklore says that some giants or trolls carried the rock to the forest and balanced it on its plinth. These days geologists say it was deposited by a retreating glacier at the end of the last ice age — and as we know, a glacier is basically the only thing as strong as a giant or a troll.