Paris rewards those who wander. Beyond the obligatory Eiffel Tower and Louvre (book tickets in advance — queues without are brutal), the city is best experienced neighborhood by neighborhood. Le Marais has the Picasso Museum, Place des Vosges, and the best falafel in Europe on Rue des Rosiers. Saint-Germain-des-Prés is for literary café culture. Montmartre's steep streets lead to Sacré-Cœur and artists' studios.
The Musée d'Orsay houses the world's finest Impressionist collection. Père Lachaise cemetery is a surprisingly moving afternoon. Day trips to Versailles, Giverny (Monet's garden), and the Loire Valley chateaux are within 1-2 hours. The Seine riverbanks are UNESCO-listed — walk them at sunset.