Anything by Sergei Rachmaninoff.
I play the piano well enough to impress my youngest students, but that’s about where it ends. From my understanding of piano literature, Rachmaninoff is a “biggie” (fancy musical term for “that’s really impressive and hard stuff, man”). I figure, if I could play something by Rachmaninoff, then I could play just about anything, right?
Well, here is a sample: