Proper noun
Niflheim
(Norse mythology) In Germanic and Norse cosmology, the Norse underworld, location of the domain Hel and of the realm of Hel, the goddess of the dead.
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. Source: Internet
This is the only instance in which Niflheim and Hel are equated (the Poetic Edda mentions Hel but doesn't say anything about Niflheim). Source: Internet
This technically makes it both Múspelheim and Niflheim in one. Source: Internet