Procure a map for free from the tourist information offices. There's an office near the cathedral in the zocalo, inside the lobby of the Museum of Oaxacan Painters. Your tour of Oaxaca city's chocolate factories is going to take you out of the main tourist center, albeit only by a few blocks. Focus on the streets that are south of the zocalo, radiating from the Benito Juarez and 20 de Noviembre markets. Many of these streets are home to storefronts that create incredible sauces, powders and pastes for Oaxaca's famous mole and chocolate dishes. The key spot is Calle Mina, or Mina Street, a few blocks south of Benito Juarez Market.
Proceed with moderation. Mina Street exemplifies the Mexican phenomenon of attracting many versions of the same type of business. Hence you'll have the popular brassiere block in Mexico City or the alley of flower-sellers in Guanajuato. Mina Street boasts all the major players in the Oaxacan chocolate empire, such as Mayordomo, Guelaguetza and the special Soledad, named for Oaxaca's patron saint, the Virgin of Solitude.
Follow your nose. Let the smell of cacao and spices draw you into the factory of your choice. Here you will see the process in action as workers grind together the roasted beans with other ingredients to make a variety of recipes. To seek the workers meting out the ingredients and creating the chocolate is to appreciate its art. If you speak even a little Spanish, feel free to ask questions about the chocolate. Free samples are the norm here, particularly at Soledad.
Hit the markets. Now that you have had a chance to see the factories and perhaps make a few dozen purchases, you can also find the small stalls at Benito Juarez and 20 de Noviembre markets. Some gourmands swear by the artisan chocolate sold there, though others say that Mina Street is the prime destination. Why not decide for yourself? The hot chocolate served at the 20 de Noviembre Market's Comedor María Cristina is supposed to be excellent. The foodies at Chowhound swear by the chocolate at Benito Juarez Market's La Tonita. The Abastos Market has a whole section devoted to chocolate.
Eat your chocolate Oaxacan style. The classic method of consuming Oaxaca's strong chocolate is to drink it. You can have it melted into milk or water, and the latter option will allow the flavors to shine through. Many cafes serve the hot chocolate with pan de yema, a special bread for dunking that absorbs the fluid well. Other permutations of Oaxacan chocolate are in coffee drinks, in mole sauces, inside sweet tamales and in tejate, a complex indigenous beverage that is often made at the markets.