El Rastro
Named for the arrastre (dragging) of animals in and out of the slaughterhouse that once stood here and, specifically, the rastro (blood trail) left behind, this site explodes into a rollicking flea market every Sunday 9–3 with dozens and dozens of street vendors with truly bizarre bric-a-brac ranging from costume earrings to mailed postcards and thrown-out love letters. There are also more formal shops, where it's easy to turn up treasures such as old iron grillwork, a marble tabletop, or a gilt picture frame. The shops (not the vendors) are open during the week, allowing for quieter and more serious bargaining. Even so, people-watching on Sunday is the best part.