John Cale took part in an infamous 18-hour performance of Erik Satie's "Vexations". While there is no recording of that performance (think of all that tape!), a video has emerged that's quite fascinating. Others have called it "astonishing", "jaw-dropping", "priceless." And I can't disagree - try to think of a network or channel that would play this today.
I've mentioned it before, and still don't really know what I think about the thing. It's certainly hypnotic, and enjoyable enough - it has that great late 19th-century crepuscular French mystic mood going, and that's worth something. You can read fascinating notes on the piece by a pianist who performed it in totum with only one partner, or the opaque Wikipedia entry on the piece, too, if you want a variety of nearly baseless speculation.
Try putting it on repeat, and see what you think after 840 playthroughs (to be honest, I'm not sure whether he plays one cycle or three). Volunteer for this experiment by downloading it here. The audience's titters may be distracting at first, but I find that they ultimately blend in well with the music, giving it some texture. God I'm being pretentious. Let me know how you make out, OK?