A public square a few streets away from Montmartre's Sacré Cœur. Avoid eating at the restaurants there (sit for a coffee or a glass of wine, though). Also, avoid getting a portrait done unless you know exactly how much you'll be charged! This square was historically world-famous for its painters, cafés, and ambiance. It's very charming, so take a walk, take it all in, and avoid the many tourist traps ;)