Le musée d’Orsay is my favourite museum, point final. It was a railway station for less than 100 years (construction finished in 1900) before being abandoned. It was used by Orson Welles in 1962 as a set for his film version of Franz Kafka’s “The Trial” before eventually being turned into a museum that opened in 1986. Wikipedia has an interesting article on the history of the building.
It is full of mainly French art dating from 1848 to 1915, including painting, sculpture, furniture, and photography.
62, rue de Lille, 75343
M° Solférino, RER C Musée d’Orsay