How hard is Beethoven's moonlight sonata 3rd movement?

It's a huge jump from Rach prelude and Clair de Lune, but it's a step down from Hungarian Rhapsody (are you sure it's an "intermediate piece?") In terms of Beethoven piano works, the 3rd mvt is around late intermediate to early advanced. I recommend you learn a few Beethoven sonatas before trying this one. I recommend the 3rd mvt of the Tempest Op. 31 no. 2, The 1st mvt of Op. 31 no. 1. Op. 10 no. 1, Op. 2 no. 1, Op. 2 no. 2, and maybe the 2nd and 3rd mvts of the Pathetique Op. 13. The 1st mvt of the Pathetique is a little easier than the Moonlight 3rd, but it's still up there in late intermediate Beethoven.