It's the long lost clean-out/drain plug described in the Viking runes that have long mystified scholars. According to Norse legend, Kraksho, the Asgaard giant in charge of plumbing and sanitation installed the drain to middle earth in case global warming caused the seas to rise and threaten to flood the fjords. Like Thor's mighty hammer Kraksho's giant magic wrench would save the day.
This illustration records Krahsho inspecting the installation of the drain. Sadly there's no scale reference to indicate the massive size of the giant.
Scientists imagine the giant circular object once uncovered will appear to be something like this.
