The largest antique market in the world takes place every weekend as well over 100,000 people stream in the Les Puces de Saint-Ouen, commonly called "Les Puces" (fleas) or the Clignacourt market. Covering over 17 acres, the market is a hodgepodge of vendors, some in stalls, some in shops. There's an app you can download to help make sense of the various markets within the market. Metro: Porte de Clignancourt, Line 4. Open Saturdays and Sundays. Some shops are also open on Monday. Need we say watch your wallet, credit card and mobile and leave your passport at home?