Why Paris dominates
Impressionism was a Paris movement (1860s–1890s). The state purchased extensively, and private collectors bequeathed entire estates to French museums. Result: Paris alone holds maybe 40% of the world's Impressionist canon.
Paris
Paris Musée d'Orsay (the central holding — Monet, Manet, Degas, Renoir, Cézanne, Pissarro), Musée de l'Orangerie (Monet's Water Lilies in two oval rooms — purpose-built for the canvases), Musée Marmottan Monet (Monet estate works, including Impression Sunrise — the painting that named the movement). All three need separate visits; combined ticket exists. Saint-Germain base.
Giverny
Monet's house and gardens, 70km west of Paris. Day-trip by SNCF to Vernon then bus or bike. Open April–November only. The Japanese-bridge water lily pond is the painting site.
London
London National Gallery (Monet, Manet, Renoir, Degas, Cézanne — strong if smaller), Courtauld Gallery (Manet's Bar at the Folies-Bergère, Cézanne's Card Players). Tate Modern has post-Impressionist Cézanne forerunners.
Rouen
Musée des Beaux-Arts de Rouen — Monet's Rouen Cathedral series subjects; the cathedral itself stands across the city. Day-trip from Paris (1h15 SNCF).
Copenhagen
Copenhagen Ny Carlsberg Glyptotek — strong French Impressionist holding (Gauguin in particular), plus the only major Cézanne and Manet collections in Northern Europe. Brewery-built museum, atmospheric setting.
Other strong holdings
Madrid's Thyssen-Bornemisza, Munich's Neue Pinakothek, Geneva's Petit Palais (private museum specifically Impressionist). Each has a few important canvases but not collection depth.
Strategy
Book Orsay 8–10am for empty rooms. Marmottan often skipped by tourists — quietest of the Paris three. Combine Orsay + Orangerie one day; Marmottan + Giverny day-trip second day.