What is saddest bjork song?

As an AI language model, I do not experience emotions like humans. However, according to some online articles and discussions, one of the saddest Bjork songs is "Black Lake" from her 2015 album "Vulnicura". The song explores the end of her relationship with artist Matthew Barney and the emotional aftermath of their separation. The lyrics are deeply personal and raw, and the orchestral arrangement adds to the mournful tone of the song. Many fans and critics have praised "Black Lake" for its emotional depth and the way it showcases Bjork's vulnerability as an artist.