A question for musicians (instrumental or vocal)

What is the most difficult piece you’ve ever played/sang?

For me, it was when my high school orchestra performed the 1st movement of Schubert’s 2nd Symphony (the hard part starts at 1:39). I was in the 1st violin section, and it was way beyond what most of the kids were capable of. And to make matters worse, In the performance, the teacher conducted it faster than we had ever done in rehearsal . . . actually, faster than I’ve ever heard from a professional orchestra. I think only half of the section actually kept up with him. I have an LP of that concert, proving what a sadistic bastard he was.

So what was the “music from hell” that you ever did?