Rick's flagship Paris walk through the oldest part of the city, about 3 miles covering roughly 2,000 years of history (the audio runs ~73 minutes; allow a couple of hours on foot, more if you go inside the sights). It starts at Notre-Dame and the Deportation Memorial behind it, loops around the Île de la Cité, crosses to the Left Bank and the Latin Quarter (Saint-Séverin, Place Saint-Michel, the Shakespeare & Co. quarter), then returns to the island for Sainte-Chapelle and the Conciergerie, finishing near the Pont Neuf.
A great first-day orientation, and it overlaps with our Notre-Dame and Sainte-Chapelle stops. Free from Rick Steves Audio Europe; the route map (PDF) is on this page.