For years I would go to Paris, armed with a guide book, and experienced the most wonderful city in the world. Today, in addition to using guide books, phone apps, and audio guides, people tour Paris on their own. However, in order to get the most out of a trip to Paris, hire a professional, licensed tour guides. In order to be a licensed tour guide (and they do need to be licensed), a guide goes through a rigorous process of being certified. See the blog post for recommendations on Paris tour guides.