Graffiti doesn’t always spoil buildings. In fact, it’s the only way to improve a lot of them.

Last weekend saw a tunnel in Leake Street, near Waterloo, transformed into an oasis of colors by graffiti artist Banksy for the Cans Festival. The exhibition, which lasted three days, encouraged people to add to the art with their own stenciling.

There are some excellent photos in this Flickr photoset. Check out the site of the festival for more information.