So, in the early 1990s composer Marc-André Hamelin decided to create a piece of piano music specifically for the player piano. How is it specifically for the player piano? Well, it is completely impossible for a single person to play this. Several might be able to do it, but then it wouldn't be played as intended. Here's a MIDI rendition, along with the sheet music. Now, I'm sheet-music-illiterate -- I got out of Music Appreciation in high school with my school's equivalent of a gentleman's C (meaning I made it clear that having me repeat the class would be to no one's benefit at all) -- but you can plainly see the complexity.
Of course, it's not the same without seeing it on an actual player piano. Or, more specifically, an actual player piano that looks as if it's possessed by ADHD-riddled ghosts trying to chase a cat off the keys: