Clair de Lune, La Mer, etc., by Claude Debussy, some of my favorite pieces.
Debussy was categorized as Impressionist writing, which was an era of art in his day with the idea of painting an emotion or to evoke a feeling of a scene, and not about portraying something in the realistic accurate sense. Oil painters like Monet, Renoir, Vincent van Gogh, were Impressionist painters. Renoir's paintings look out of focus, because his eyesight was nearsighted, but it worked for the Impressionist style. Music written in similar loose terms was classified as Impressionist based on those kind of ideas (Debussy, Ravel, Dukas, Satie, Manuel de Falla, etc.).
Debussy was loose on traditional functional harmony that previous composers all relied upon. He often used parallel chord progressions, whole-tone scale, harmonic devices which defy the use of traditional functional music theory. If you try to figure out Debussy's harmony thinking in traditional harmonized scale chords forget it. The way he used chords was more in an interval relative sense instead of major or minor scale harmonized chords.
Lot of Jazz musicians study Debussy, because of his harmonic approach really is very similar to how Jazz harmony works.