Le jardin du Luxembourg is a favorite haunt of mine. See if you can find the Statue of Liberty replica in the garden there are usually art exhibits in the garden itself
Musee de Branley - great artifacts of colonial rule - things typically not seen in the US (Alma Marceau)
How about a movie (sub-titled in French) at one of the old theatres in the Latin Quarter (Metro Odeon). Even better - go the the Grand Rex (Metro Bonne Nouvelle) - largest cinema theatre in Europe seating 5,000.
La Defense wonderful statue exhibits along the Esplanade with a great view of the Arc de Triomphe. (There is a large shopping complex at the Grande Arche) Ligne 1 (Metro Esplanade de la Defenst et La Defense)
What about a day in Bois de Bologne - rent a boat and sit on the water. Metro 9 - La Muette
Crepe maker at the exit of Saint Placide Metro (linge 4)
Bar hop in Montparnasse - Metro Edgar Quinet live jazz
Exhibits at the Biliotheque Nationale de France (BNF line 14) or at UNESCO - Metro Segur