Châtelet–Les Halles station
Châtelet - Les Halles is a major subway hub in Paris. With almost one million users per day, it is probably the world's busiest subway station after Shinjuku station in Tokyo. Although the station functions as a single unit, strictly speaking it is two. It is named after the Châtelet monument and the former market of Les Halles, and the underground concourse contains both their metro stations. The RER station is at Les Halles while the metro lines are served by Châtelet, except line 4 which stops at both.