Of the two islands in the Seine River within the city center of Paris, Île de la Cité is the more famous; it's the one that has Notre Dame and the Pont Neuf. But Île Saint-Louis is nothing short of a Parisian dream. It's hard to believe it was once for cattle grazing!
Connected both to the Right Bank and Île de la Cité by five bridges, Île Saint-Louis has tiny, quiet streets that all end with great views. It's also home to Berthillon, the famous ice cream maker whose creamy flavors are also sold in cafes on the island, unique and surprisingly affordable gift shops, galleries and a small-neighborhood vibe that doesn't feel like anyplace else in the City of Light.
There are no Metro stops on the island itself; the M7's Pont Marie is your best bet, as you come up right at the Pont Marie on the Right Bank. Be careful crossing here, as traffic seems to come from all sides.