Gare du Nord

In terms of passenger traffic, the Gare du Nord is the major railway network SNCF (grandes lignes). It's located in the 10th arrondissement of Paris.

The trains run locally, nationally and internationally.

Internationally, the trains go to the United kingdom via Eurostar, to Belgium, Germany and the Netherlands via Thalys.

Nationally, it's the major station to go to the North, the french regions North-Pas-de-Calais and Picardie (North of France), the trains from Gare du Nord serve the majority of the big agglomerations of those 2 regions.

Locally, the RER B goes on the platform 42 (to the south)  and 43 (to the north) while the RER D goes on the platform 41 (to the north) and 44 (to the south).The platforms pull in the four-lane underground stations
The frequency can reach 3 minutes for the RER B, in rush hours and 5 minutes for the RER D.
At ''Gare de Magenta'', the RER E is connected to the Gare du Nord by an underground access.

You can also go and visit Paris from/to the Gare du Nord by the Paris metro line 4 and the Paris metro line 5, by stopping to the Gare du Nord station. The traffic is heavy with a frequency of 3-5 minutes during the day for the metro line 4, and 2-4 minutes for the metro line 5, for the week.
The Gare du nord is also connected with the Paris metro line 2,  via a connecting corridor between Chapelle station (line 2) and the underground part of the Gare du nord.

In addition to those trains, you can also visit Paris from the Gare du Nord by bus, Paris l'Open tour, the Noctilien bus (bus by night), as well as some lines of the transilien (H and K, the transilien is the SNCF railways network).