Two formats
Working-factory museums (you watch chocolate being made) vs history-and-tasting museums (curated displays + sample bars). Both formats below; pick by interest.
Cologne
Cologne Imhoff-Schokoladenmuseum (Imhoff Chocolate Museum) — built into a working chocolate factory on Rhine peninsula. Watch tempering and molding live; integrated tasting fountain. €15 entry, daily. Altstadt walking distance.
Bruges
Bruges Choco-Story Brugge — strong on Belgian chocolate history, demonstrations, tasting. €10 entry. Less working-factory than Cologne; more story-museum.
Zurich
Zurich Lindt Home of Chocolate (2020, opened on Lindt's actual factory grounds, 30 min from Zurich center). World's largest chocolate fountain (9 meters), tasting bar with unlimited Lindor truffle samples. €15. Suburban location requires train + walk.
Brussels
Brussels Choco-Story Brussels (similar group as Bruges). Plus Galler, Neuhaus, Pierre Marcolini, Mary Chocolatier flagship shops in Centre Historique — practically a chocolate tour without museum entry.
Barcelona
Barcelona Museu de la Xocolata (Sant Pere) — Spanish chocolate-history focus. €6. Less impressive than Northern European; combined with admission to El Born walking tour.
Paris
Paris Choco-Story Paris (similar chain). Plus chocolate boutique tours (Patrick Roger, Pierre Hermé, Jean-Paul Hévin) deliver more in 90 minutes than most museums.
Strategy
Combine museum + boutique-shopping for half-day "chocolate tour." Best for kids in Cologne (factory floor) or Zurich (fountain). Avoid summer weekends — long queues at popular museums.