To answer Houndstoot's comment about
Until recently, street artists were allowed to paint on shop shutters. Apparently, this is no longer the case, see this article. Too bad, because those shutters were protected from wild art, and were fun to search for.
Neki, maybe you can tell us more about graffiti in Barcelona? As a visitor, I like them, but as a resident, you may have another opinion?
Here are a few more pictures from previous trips: