"When La Monte Young Says 'Take It From the Top', He Means Last Tuesday"
This joke that a music critic once made in a review of Young's music most easily applies to his magnum opus, the Well-Tuned Piano. In its longest performance, its takes six consecutive hours to perform, so it is probably the longest piano solo in the history of music. (Young is the only one who has played it so far.) He actually said in an interview that he doesn't even bother getting out of bed the day after its performance.
What is so special about this piece, then? Two words: just intonation. Young takes the most Western of instruments and retunes it according to Eastern and ancient scales. (Go here is you want the nuts and bolts of it.) The affect is beautiful and other-worldly, both familiar and utterly strange at the same time. The shift between meditative chords, the sonic assaults, and purity of sound makes this by far a masterpiece of human creativity. It is taking something that all are familiar with and transforming it into something even more beautiful.
Don't try and find it anywhere though. The CD recording issued in 1992 was five discs and can fetch up to $900! The one disc DVD sells on Young's website now for over $200. The only way I can listen to it is because the music library here at Berkeley has a copy. But if you do find it, it is well worth listening to.