The Musée d'Arts de Nantes (formerly the Musée des Beaux-Arts) houses one of the most important fine art collections outside Paris, covering European painting from the 13th century to the present. The original 19th-century building was extended in 2017 with a new wing by the architect Stanton Williams, and the result is a thoughtfully integrated complex that works well for both the old and modern collections.
The highlights include works by Rubens, Caravaggio, Ingres, Monet, and Kandinsky, and the 20th and 21st century galleries are consistently strong. The museum is well run, with good temporary exhibitions and a pleasant ground-floor café. It's worth two hours at a minimum.