Musée d'Orsay

The Gare d'Orsay opened in 1900 as a state-of-the-art railway terminus for the Paris World's Fair, built for the new electric trains that made steam-era station design (with its smoke-filled train sheds) obsolete overnight. Within a few decades the platforms were too short for modern trains, and the building drifted into use as a mailing centre and film set before a 1970s campaign saved it from demolition and converted it into a museum, which opened in 1986.

What makes the Orsay essential isn't just the building — a soaring iron-and-glass hall with a giant station clock still mounted on the facade — but the collection inside it: the single best concentration of Impressionist and Post-Impressionist painting anywhere, covering the period (roughly 1848 to 1914) that falls between the Louvre's cutoff and the Pompidou's start. Monet, Renoir, Degas, Manet, Cézanne, Van Gogh and Gauguin are all represented in depth, not just a token painting or two.