One of the largest flea markets in the world, selling everything from second-hand prints to furniture, Le Marché aux Puces de Saint-Ouen attracts nearly 200,000 visitors each weekend. Boasting more than 2,500 stalls, there is not enough time in one day to explore the entire market. Open every Saturday and Sunday from 10 AM to 6 PM and every Monday from 11 AM to 5 PM, the market is undoubtedly one of the best free things that you need to add to your itinerary.