Cobblestones is a popular but slightly incorrect term for what the French and Belgians call pavé. Stickly speaking they are setts, usually of granite and more regular than cobbles, which are, or were, water-formed stones.

We usually call them cobbles, though. My street here in Hull is cobbled (it's one of the medieval streets in the Old Town), and I can assure you that cycling is no fun at all.