Sainte-Chapelle is hands down one of the best chapels that I have ever been to. You'll see loads of pretty churches and stained glass windows throughout Europe, but Sainte-Chapelle is a bit more off the beaten bath. The reason Sainte-Chapelle is a standout is because the entire top floor is made out of literally all stained glass windows. Epically beautiful and a spot you won't want to miss in Paris.