John Mark Harris arranged a piece for piano by Iannis Xenakis to make it, y’know, playable by a human. You can see and hear the graph for Evryali.
Harris comments:

The title refers to the “Medusa, with head of writing snakes”, as well as “the open sea”. Both allusions have clear meanings upon hearing the piece…

Evryali was composed without regard to the limitations of the human anatomy, as the branching often expands beyond the range of two human hands. In more than one instance, the branching has caused bushed to appear at the extreme right and left of the keyboard, yet there are also bushes in the center of the piano. The performer must obviously edit the score. The graph I made became a tool for determining what I would leave out…

The music that remains, after editing, is anatomically possible. Yet the performer is left with an undertaking that can not be thought of as reasonable. The relentless repetitive motions, wide leaps, and awkward streams of chords directly challenge the pianist’s need for fluid fingers and free arms. The pianist runs the risk of gazing into Medusa and freezing solid. Brute force and physical endurance are not enough to solve the difficulty. Only through the same imagination that one finds the music “possible” can one find the answer to its realization.

As one can never view Medusa directly, without cheating in the manner of Perseus, one can never hear the piece performed exactly as composed. The audience is not granted a true image of Evryali, but must, like Perseus, experience only a reflection of the monstrosity.

Further commentary from Marc Couroux:

Evryali is not virtuosic, nor is it anti-virtuosic. It is highly unlikely that this state could have come about as a result of the composer’s insufficient command of pianistic technique. The gauntlet is so clearly thrown down that the difficulties cannot be anything other than premeditated… The fact that one cannot physically realize the totality of Evryali makes it seem unnecessarily utopian. The task of any performer is to strive, regardless of difficulty, to achieve every detail and to project them into a broader context.

[via phil harnish]