Marseille - bikes for hire

All throughout the major European cities, we saw bikes for hire from local government authorities. I am still not sure how they work, you have to pay for their hire at a centralised machine and it unlocks the bike from its stand.

I imagine you can only pay via credit card and that becomes your identification check, I am still unsure if you have to return the bike to its original location or to one of the numerous racks around the city, needless to say, these bikes are very popular as you see them being ridden around all over the place.