Inside a giant igloo in a snowy Norwegian village on Feb. 2, the sound of a horn rang out, warming the mood of a freezing audience, huddled together in -24 Celsius weather. But the four musicians performing are even colder: the instruments they are playing are all made of ice. The xylophone, claves and wind instruments were all painstakingly carved from ice blocks extracted from a frozen lake, and are part of a finger-numbing performance at the 13th Ice Music Festival in the mountain village of Finse.