Marc-André Hamelin’s piano piece Circus Galop cannot be played by a human. It was not written with humans in mind.
The piece is fast and frenetic enough to be technically challenging for a human player, but at several points enough notes are being played at the same time to make it impossible for a single pianist to play it. We only have ten fingers, you see.
It’s not entirely impossible, though! One arrangement allows five people – ten hands, one hundred fingers – to perform it together. On one piano, of course. Also it involves blindfolds and juggling balls for some reason:
And if you can deal with some bad language, check out this guy performing Circus Galop on a Guitar Hero-like program called Clone Hero: