This is perhaps one of the most amazing impromptu acoustic performances ever caught on film. French music blog gods La Blogotheque captured Sigur Ros performing Vid spilum endalaust in a small cafe in Paris on mostly borrowed acoustic instruments. The whole story of how they arranged for this to happen and the reaction of the people quietly eating their meals is detailed in their story. You can also see on the video the waiters going back and forth and various people completely ignoring the amazing concert going on around them. Take a look, it's incredible.
La Blogotheque Sigur Ros Article