A mason came and made a deal with the Norse gods to build them a great (but expensive) wall to protect Asgard from the enemies outside. Loki drove an even harder bargain. Would the mason be able to complete the wall under the extreme restrictions from the gods? The mythological tale gets a little crazy at the end, and you do not want to miss the punch line. The original saga probably didn’t refer to it as a punch line, but that’s the way it comes across.