Gare du Nord is a Paris Métro station, and serving line 4 and line 5. It is the busiest station in the system (not including RER), with 48 million entrances a year. It is connected to the SNCF's major station, Gare du Nord, literally, Station of the North, which serves RER lines B and D and Transilien Nord commuter trains as well as interurban trains to northern France, Eurostar trains to London and Thalys trains to Brussels, Amsterdam and Cologne.