Versailles, perhaps the world's largest palace, makes a good day trip from Paris. The most convenient way of getting there by pubic transportation is the suburban RER C train that goes along the Left Bank. Buy a "Paris-Versailles Rive Gauche" ticket for the 20-minute ride. Wear good walking shoes. The palace is about a 10-minute walk from the station (the last on the line) and that's just the beginning. You won't want to miss the Hall of Mirrors where the Treaty of Versailles was signed ending WW I or the gardens designed by André Le Nôtre or Marie Antoinette's Petit Trianon. Various tours can also be arranged from Paris.