Begin your day with a leisurely breakfast at the Café de Flore (#172 boulevard Saint-Germain), and afterwards walk one block west until you reach the large square featuring the 11th-century church of Saint-Germain-des-Pres. One of the most famous churches in Paris, it exhibits a severe Romanesque beauty.
Cross the Boulevard Saint-Germain and head down the Rue Bonaparte to Pierre Hermé’s beautiful pastry shop (#72). Hermé is one of the country's great pastry makers, and he’s famous for his superb macarons, which come in a tantalizing variety of flavors and make a wonderful gift. Continue walking south along the Rue Bonaparte to the beautiful Place Saint-Sulpice. Here you'll find a wonderful fountain guarded by large stone lions and a church with murals by Delacroix. After a stroll around the square and a peek inside the church, walk west on the Rue du Vieux Colombier until you reach the Rue de Sèvres.
Turn left on the Rue de Sèvres and walk two blocks to La Grande Epicerie, the food hall of the famous Le Bon Marché department store. This is one of the most luxurious food stores in Paris; the locals prefer to shop here instead of at better-known but decidedly touristy Hediard and Fauchon, both on the Right Bank. It's an excellent place to pick up hard-to-find items for your larder back home such as herbes de Provence or bouquet garni.
Exiting the Grand Epicerie onto the Rue de Sèvres, walk west on the same side of the street until you reach Quatrehomme (#62). This is one of the world’s great cheese shops and a fascinating address for anyone who wants to deepen their knowledge of French cheeses. They are happy to offer tastes and can "cyrovac" cheese for travel. Further down the Rue de Sèvres, cross the street and walk up the pretty little Rue Mayet until you reach the Rue du Cherche-Midi, one of the Left Bank's most emblematic streets. There is some wonderful window-shopping here.
Turn left and walk four blocks to Le Nemrod, a bustling café that’s very popular with locals. I recommend the croque monsieur (grilled ham-and-cheese sandwich served with salad), one of their excellent salads or a steak tartare. After lunch, head north on the Rue Saint-Placide to the Rue de Sèvres and cross the street, where the Rue Saint-Placide becomes the Rue du Bac.
Continue walking along the Rue du Bac as it passes between the two buildings of the Bon Marché department store. If you’re curious about the crowds on the left side of the street, you might want to visit La Chapelle de la Médaille Miraculeuse, which is run by a local convent. As the story goes, a pious young woman named Catherine Labouré had a vision of the Virgin on this spot in 1830, and acted on the Virgin’s instructions that a gold medal be cast in her image. The chapel is one of the most-visited pilgrimage sites in France. Crossing the Rue de Babylone, you might want to stop for an ice cream cone at the excellent Bac à Glaces (#109), and enjoy it in the small public garden just next door.
Continue along the Rue du Bac to the Pâtisserie des Rêves (#93). Run by celebrated pastry chef Philippe Conticini, this recently opened shop is one of the prettiest pâtisseries in Paris, and the beautiful pastries are displayed under heavy glass cloche, or bells, on suspension pulleys.
Continue north on the Rue du Bac to Ryst-Dupeyron (#79). Best-known for its vintage Armagnac and Cognac (the family who owns the shop has been Armagnac merchants for four generations), this is an excellent spot to do what Parisians do — pick up a bottle of spirits from your birth year. It also carries a superb assortment of wines.
Next, you may want to turn right on the Rue de Grenelle and visit the quirky Musée Maillol (#59-61), which was founded by Dina Vierny as an homage to the sculptor Aristide Maillol. In addition to Maillol, this intimate gallery also exhibits works by Degas, Rodin, Picasso and Cézanne.
If you’re not in a museum-going mood, head to Barthélemy (#51). This tiny shop is sort of an Ali Baba's cave for cheese-lovers and supplies a number of well-known Left Bank residents. (Note that on Tuesday and Friday mornings you could also add the open-air market on the Boulevard Raspail to this walk, fitting it in between Pierre Hermé and La Grande Epicerie. The market begins at the corner of the Rue de Sèvres and runs south on the wide median strip in the middle of the Boulevard Raspail.)
Excerpted from Andrew Harper's Paris, a free app for the iPhone and iPad.