This is the most interesting part of the fifth: a pleasant mix of architecture, intellectual vibes, greenery, cute traditional cafés and tiny indie movie houses. From the stately Panthéon, the final resting place of greats like Marie Curie, Voltaire and Josephine Baker, head down iconic Rue Mouffetard and its side streets. Then go back up to Rue Monge and check out the Arènes de Lutèce (a Roman theater ruin) and Jardin des Plantes. Have a seat in the elegant café at the Grande Mosquée for mint tea and middle-eastern pastries.