I am wondering if there are any accounts of theories or myths about what lay in or beyond the White and North seas? Considering the Nordics/Finnics/Rus were trading in the White Sea and in the case of the former, actually colonizing as far north as Greenland and Iceland, surely they gave it some thought? Perhaps the Inuit or residents of Siberia pondered it as well?
Finns and various other Finnic peoples, e.g Samis, Mordvin, Erzya, etc believed the underworld, the world of the dead, to be located in the north. This is mentioned in, for example, the Mordvin epic Mastorava, Finnish epic Kalevala. As for non-mythical or non-religious ponderings, I do not know of any.