Waterfall (seen left) is one of many iconic lithographs by M.C. Escher. In the image, water is seen apparently running uphll before pouring off the edge and to a waterwheel. The theory behind it is that as the water falls from the top of the waterfall, it will strike the waterwheel.
Basically it’s just the concept of perpetual motion. The current works to fight against the eventual and unavoidable evaporation of the water, and with the water striking the wheel that current could maintain itself indefinitely. Unless you knocked the contraption down, of course, but that’d just be mean.
For a long time, people saw this as nothing but a clever optical illusion. But one intrepid soul, YouTube user “mcwolles,” looked upon this image and said (presumably in a loud, strong voice): “I can do that.”
And he did.
I won’t lie: I kind of want one to display on my dining room table.