I know organ music is not everybody's cup of tea here, but I'm proud to have at last completed Bach's Clavier Übung III, also known as the German organ Mass (completed, but not done.... a couple of items badly need to be rerecorded). This ingenious chorale Bach - BWV 682 - Clavier Übung III - Vater unser im Himmelreich(8:37) took me an awful long time to get the hang of. Generally considered Bach's most difficult chorale, it may sound quite laid back but it's a mighty complex and demanding thing, boasting two different rhythms (triplets against a Lombardic step), a walking pedal bass, and two voices in the middle singing the cantus firmus in canon. The occasional dissonances that are necessarily created by the voices grinding against each other are just amazing. Nobody but Bach could have created something like this.