The Vélib public bicycle scheme is fantastic! There are 20,000 bikes throughout the city, and you can use them whenever you want. For a half-hour rental, the cost is one Euro, and goes up from there. You do have to use your credit card (must have a microchip in it) to check them out, and you do have to agree to a 150 Euro charge, should the bike not be returned or be damaged during your use. The cost for not returning the bike at the end of the first half hour mounts quickly, but the cost for regular use just can’t be beat! And, the bike posts are no more than 300 meters apart throughout the city.