I'm actually only referring to a couple of places in Prelude in C# minor. Most of the song is "almost impossible" for one reason or another, but there are a couple of places near the end where the lower octaves and the upper freakish chords are played simultaneously. The 9th and 11th measure from the end, to be precise. Even Rachmaninoff with his freak hands had to roll that.
It's not a song, it's a prelude. And actually not very technically difficult, one reason for its immediate and enduring popularity. The simultaneous chords are just played very quickly one after the other and not "rolled".
"not very technically difficult" is a matter of perspective. It's about as difficult a piece as any student or amateur is ever going to play or be exposed to and few students or amateurs are skilled enough to play it.
But it is accessible to amateurs, and sounds very impressive. Which is, as you noted, a good reason why it's so popular. It's a good piece to pull out when you want to show off.
