What is "niflheim"

Niflheim (or Niflheimr) ("Mist Home", the "Abode of Mist" or "Mist World" , or probably world of the darkness according to the Oxford English Dictionary) is one of the Nine Worlds and is a location in Norse mythology which sometimes overlaps with the notions of Niflhel and Hel. The name Niflheimr only appears in two extant sources: Gylfaginning and the much-debated Hrafnagaldr Óðins.

Niflheim was primarily a realm of primordial ice and cold, with the frozen river of Elivágar and the well of Hvergelmir, from which come all the rivers. According to Gylfaginning, Niflheim was one of the two primordial realms, the other one being Muspelheim, the realm of fire. Between these two realms of cold and heat, creation began when its waters mixed with the heat of Muspelheim to form a "creating steam". Later, it became the abode of Hel, a goddess daughter of Loki, and the afterlife for her subjects, those who did not die a heroic or notable death.