At box #15 at the Mercato di Testaccio, two former retirees serve some of Rome's best sandwiches - they're filled with Roman classics like carciofi alla romana (artichokes simmered with herbs), picchiapò (shredded brisket in a tomato and onion sauce), and pajata (intestines of suckling veal cooked in tomato sauce). Be sure to take a number when the stall is crowded and after you collect your order, grab a bench beside the stall and get to business.