If you’re spending a few days in town you can easily rent a bike. There are numerous places around town. But if you are staying a few weeks or more buying a second hand bike is more economical. At Fiets+Meer they sell more than 300 of them. If you buy one here you’ll get half of the price you’ve paid back when you return your bike (evidently in good shape). So you can buy a great bike for 130€ and receive 65€ in return when you leave the city, now that’s a great deal.