Whilst Krakow might not be at quite the same level as Amsterdam, an increasing number of both locals and tourists are favouring bikes at the most efficient way of getting around town. A semi-pedestrianised Old Town and good cycling paths by the river make for stressfree experience on two wheels, and the compact nature of the city as a whole means you're able to take in pretty much everything in the course of a day! The good people at Cruising Krakow will rent you a very trendy beach cruiser for a mere 10PLN for three hours, or if you fancy doing a bit of off-roading then mountain bike hire will cost you 20PLN. Find their outlet just north of the Planty in the Old Town. Alernatively join them for a bike tour.
