One of the finest music critics is Charles Rosen who is both an expert pianist and the writer of several extraordinary books on music. One of them, The Romantic Generation, has helped me to understand 19th century music (not one of my first loves). One of the pieces he discusses is the finale to Chopin's B flat minor piano sonata. In this clip, it is preceded by the previous movement, the well-known funeral march. The finale itself, a mad gallop in octaves, begins at the 9:40 mark:
What an extraodinary piece! It is like a Bach gigue for solo violin, sped up and run through a kaleidoscope of romantic harmony. That is very possibly how Chopin conceived it. Robert Schumann and quite a few others hated the piece.