The best way to describe Árstíðir, at least in this gorgeous tune, is something like what a Varangian choir might have sounded like in 13th-Century Byzantium, singing in the Hagia Sophia.
As it turns out, the tune is from the 13th Century, written by Kolbeinn Tumason. No, Wuppertal isn’t quite Byzantium, especially inside of the train station, but the lads made a mundane place seem almost holy that day.
For another, perhaps clearer version, check out this performance from Vilnius, Lithuania, in 2012. To hear this as an MP3 or FLAC file, just download the ‘name your price’ album via Bandcamp.