One my favorite day trips is to take the easy 1 ½ hour train ride up to Brussels (known as Bruxelles in French). Trains run frequently from Gare du Nord into Brussels Midi station. The round trip fare is less than $100 if you book in advance.
Brussels is a terrific walking city. It’s funky, it’s gothic, and the mussels and beer just cannot be beat. Have a Belgian waffle and bring some chocolate home with you. In many ways it is much different than Paris. English is widely spoken. For Brussels tourist info, including a map, try this link: http://www.visitbelgium.com
Here are my recommendations for things to see and do in Brussels:
Grand Place (aka Grote Markt): I love to promenade around the grandest of all squares in Europe. It is surrounded by guild houses, the Hôtel de Ville, and the Musée de la Ville. Each time I visit I discover something new.
Mannekin Pis: This is an irreverent statue of a young boy doing his business. It is certainly not in the class of the Eiffel Tower, but it might be Brussels most famous landmark. Have a chuckle, take a snapshot, and move on.
Musées Royaux des Beaux-Arts (Royal Museums of Fine Arts): This is a fine collection of mostly Belgian art, both historical and contemporary. There are works by such well-known artists as Rubens, Van Dyck, and Rembrandt. Website: http://www.fine-arts-museum.be/site/EN
Chocolate: While strolling the streets off the Grand Place notice the chocolate boutiques sprinkled about. Don’t hesitate to sample the goods but don’t overdo it, save some room for a Belgian waffle and mussels and beer later. You can always bring some chocolate back to Paris.
Mussels and Beer: Beer is a high art form in Belgium. It is only enhanced when it is paired with mussels (moules) and twice-fried fries (frites). My little slice of heaven for this delight is La Villette. Website: http://www.la-villette.be