Chartres - The 12th century cathedral of Notre Dame at Chartres is one of the highlights of Gothic architecture.60 min trainride from Gare Montparnasse
Versailles - On the SW edge of Paris, the site of the Sun King Louis XIV's magnificent palace. 20-40 min trainride by RER
Saint Denis - On the northern edge of the metropolis, site of the Stade de France and St Denis Abbey, burial place of French royalty.
Chantilly - Wonderful 17th century palace and gardens and the birthplace of whipped cream. 25 min trainride from Gare du Nord
Giverny - The inspirational house and gardens of the Impressionist painter Claude Monet are but a day-trip away. The gardens and its flowers are the most interesting part of the visit, so avoid rainy days.
Disneyland Resort Paris - In the suburb of Marne-la-Vallée, to the east of Paris, from where it can be reached by car, train, or bus the train is probably your best bet.
Fontainebleau - A lovely historical town south of Paris 55.5 km or 35 mi. It is renowned for its large and scenic Forest of Fontainebleau, a favorite weekend getaway for Parisians, as well as for the historical Château de Fontainebleau. 35 min trainride from Gare de Lyon