Along with Berlin, Barcelona is generally recognized as having the most vibrant and prolific street art scene in Europe. But unlike Berlin, Barcelona's authorities have never really embraced its graffiti culture. In early 2011, it became illegal for grafitteros to paint on persianas, the metal roller-doors that safeguard the city's stores. Predictably, the scene moved to the suburbs. But that doesn't mean there's no street art to be found in the city center. You just need to know where to look.