Vápnthjófr saga

Fact 1: Birch bark was commonly used like parchment by the vikings.

Fact 2: Gårdarike was the viking’s name for western russia.

Fact 3: Niflhel is, according to some interpretations, the lowest level of Hel, which could be concidered an equivalent of the christian hell. It was a place were bad people were punished, while helheim in general was more akin to a hades-style underworld. Or in other words: “Itching like all niflhel” = “Itching like all hell”