Beautiful and alien, Agætis Byrjun was like being plunged into an Atlantis where language, gender and songforms were largely indeterminate. Sigur Ros conjured magic with drones, using strings, brass, electronics and guitars that took Jimmy Page's bowing technique to new heights. But the showstopper was Jonsi Birgisson's otherworldly voice, swooping between tenor confessions and falsetto ballet.