Hardest piece you know?

Originally Posted by Magna Carta

A hard piece that I can play (though still learning) is the Bach Violin Ciaconna from Partita BWV 1004. Very good piece, written for the death of his cousin, Maria Barbara Bach.

...that is, if his purpose was to show himself off during her funeral.

That is a beautiful piece. I cannot wait until I learn it.

Stars and Stripes Forever arr. Guy Van Dueser

Jacobi's Sonata for Eb Alto Sax and Piano (second movement is the hardest, IMO) and Heumann's Slavonic Fantasy (another alto sax solo).

The hardest piece that I currently am able to sing is probably "Rivolgete a lui lo sguardo" which was originally from Mozart's Opera "Cosi fan Tutte". It was replaced by "Non siate ritrosi" because it was too long and in depth for a character like Guglielmo. Soon I hope to learn "Un dottor dell'armia sorte" from "Il barbiere di Siviglia". However, some of the most difficult singing I've ever done are the following:

Penderecki "Credo"
Poulenc "Gloria"
Edvard Grieg's "Fire Salmer"
Pistola in Verdi's "Falstaff"

"The One Note Song Mvmt. 1" by myself is a very challenging. You have to play it at a very quick tempo and very loudly. I've broken almost 110 strings so far in attempt to master the technique. The second and third movements are very easy, obviously because of the title, but still make excellent studies for beginning, serious piano students.

One Winged Angel from FF7 Piano Collections, pretty insane. Took half a year to learn.

As an oboest the hardest piece may be Rossini's "La Scala Di Seta"

Originally Posted by Maestro Akhil Gardner

Hardest Piece, I've played so far - Op.53, Sonata in C Major "Waldstein" - Ludwig Van Beethoven.

I would love to learn that! That's my most favorite piano solo ever. Unfortunately it’s way over my head. I’m trying to learn Debussy’s Clair de Lune and I’m having difficulty! But then I haven’t been playing the piano that long and I’m totally self-learning. Although I’m also trying to learn Mendelssohn’s Venetian Gondola Op. 30 No. 6 and I think that’s harder than Clair de Lune. Only time will tell.

As far as the hardest piece I actually know, currently it has to be Gavotte en Rondeau from Bach’s partita #3 for solo violin (arranged for guitar). I’m actually trying it on the violin too, but it’s way beyond my violin skills at the moment. I am pulling it off on the guitar, but I think I’m playing it slower than its supposed to be played. I’m surprised that I’ve gotten this far with it though, so I’m happy with the relaxed tempo.

Learning it on the guitar is actually helping me to learn it on the violin too in a way. I still have a long way to go on the violin, but playing it on the guitar gives me a feel for it and that helps on the violin even though they are totally different instruments.

The hardest thing I’ve learned on the clarinet thus far is chromatic scales. (ha ha)

Hey! They’re hard to play when you’re first starting out!

The hardest thing I’ve learned so far on the trumpet is how to oil the valves.

I've played Waldstein. Don't think it's enormously difficult really. Except that part with the trills in the 3rd movement. That gave me a bit of trouble.

I think that the most difficult piece I've played must be the Toccata in D, by Prokofiev. I would like to take it a few tics faster, but simply couldn't handle it. Argericht and Horowitz played it faster!

Indeed 2nd piano concerto by Prokofiev, especially 1st and 4th movements is insane at parts. The cadenza is HUGE and really tough, since he's trying (at least imo) to emmulate 2 piano playing, with 1 pianist... brrrr...

Also

Messiaen Vingt Regards are insane! YouTube - Messiaen: Vingt Regards - No. 6, Par lui tout a ete fait , YouTube - Messiaen - Regard de l'Esprit de Joie - Roger Muraro , YouTube - Messiaen - Regard du Père - Roger Muraro
Ligetti Devil's staircase YouTube - Greg Anderson plays Ligeti Etude 13: "The Devil's Staircase" (sorry, I couldn't find another link and you're stuck with that guy playing piano. Not that he's bad, but... the video... the tricks... )

I'll second that Prokoviev 2nd Piano concerto... INCREDIBLY difficult, particularly those cadenzas.

The only other thing I've tried to perform that is anywhere as difficult was the Ravel Concerto pour la main gauche, where ONE hand is trying to sound like two pianos. I never was able to really get that one off the ground to my satisfaction.

N.B. the above comments exclude the Ravel Piano Trio, which is, in my opinion, the single most difficult piano part to play in the entire repertoire.