Tourists are attracted to queues, art lovers to quietude. So while the mass of Monet fans visiting Paris line up outside the Musée d’Orsay and the Orangerie, connoisseurs head to the Musée Marmottan, an institution so surprisingly little known that it had to rename itself the Musée Marmottan Monet to flag up the fact that it owns the world’s largest collection of Monets.