Niflheimr is the clearest case in Norse mythology of a place that may have been invented by the man describing it.
Snorri needs it. His cosmogony in Gylfaginning runs on a symmetry: a world of fire in the south, a world of cold in the north, and the void between them where the two meet and life condenses out of the melt. Fire is Múspell, and Múspell is attested elsewhere. Cold is Niflheimr — and Niflheimr appears in no Eddic poem at all.
What the poems have is Niflhel. Vafþrúðnismál says that those who die out of Hel go down into Niflhel; Baldrs draumar uses the same term. That is a location within or beneath the realm of the dead, not a primordial cosmological pole in the north.
What Snorri builds with it
His account: Niflheimr was made many ages before the earth, and in its middle is the spring Hvergelmir, from which flow eleven rivers — the Élivágar — whose venom hardened into rime as they moved away from their source, and the rime built up layer on layer into Ginnungagap's northern part, while sparks from Múspell came up from the south, so that the part of the gap facing north was heavy with ice and the part facing south was light with fire and the middle was as mild as windless air. Where the rime met the warmth it thawed and dripped, and life quickened in the drops, and the shape was a man: Ymir.
He also puts the third root of Yggdrasil over Niflheimr, above Hvergelmir, with Níðhöggr gnawing it from below, and says Hel was thrown into Niflheimr and given authority over nine worlds there.
Nifl- is the element behind German Nebel and Latin nebula: mist, fog. Niflheimr is Mist-home, and it is one of the most evocative names in the corpus.
Why the doubt is worth taking seriously
Three things make Snorri's construction suspicious as an inherited belief.
- The word is absent from the poems. Every other major location — Ásgarðr, Jötunheimr, Miðgarðr, Múspell, Hel, Álfheimr — appears in Eddic verse. Niflheimr does not.
- The symmetry is too good. A fire pole and an ice pole with a temperate middle is a schematic, and it resembles classical and medieval Christian cosmological writing more than it resembles the loose, contradictory geography the poems actually give.
- Snorri himself is inconsistent. He uses Niflheimr and Niflhel both, does not clearly distinguish them, and in Skáldskaparmál seems to treat them differently again.
Against that: Snorri had access to poems now lost, the nifl- element is genuinely old, and Vafþrúðnismál's Niflhel shows the concept of a misty lower region existed independently. The honest position is that a cold, misty lower world is probably authentic, and that its promotion into one half of a dualistic creation scheme is probably Snorri's.
This matters for more than one place. It is the same question that hangs over the whole Prose Edda: the most systematic account of Norse mythology is also the most likely to be systematised.
Hvergelmir
The spring is the better-attested part. Grímnismál has it as the source from which all rivers flow, and says that the hart Eikþyrnir standing on Valhalla's roof drips water from his antlers down into it. Snorri says an enormous number of serpents live in it with Níðhöggr, more than any tongue can tell.
The name means "bubbling cauldron" or "roaring kettle," and in an Icelandic context hver is the ordinary word for a hot spring — the element in Geysir's neighbours and in place-names across the island. A boiling source at the root of the world, in a text written in Iceland, is not an abstract image.
The ice-hell that is not there
Niflheimr is repeatedly presented in modern material as the Norse realm of the dishonourable dead, an ice-hell, or the specific destination of those who die badly. That reading fuses Niflheimr with Hel's realm and with the corpse-shore of Völuspá, and no medieval source supports it.
In Snorri, Niflheimr is where Hel's realm is located and is not itself a punishment. Its inhabitants, apart from Hel's household and the serpents, are not described at all.
For the fire at the other end, see Surtr; for the void between, Ginnungagap; and for the Norse overview and how much of the pantheon's structure comes from one writer.
Are Niflheim and Niflhel the same place?
Snorri uses both and never distinguishes them clearly, which is itself the strongest argument that he was working with a term he had inherited and one he had adapted. Vafþrúðnismál's Niflhel is explicitly a place below Hel — a lower region for a second death, which is an idea the corpus does not otherwise develop. If they are two places, the cosmology has a basement beneath its underworld. If they are one, then Snorri's primordial ice-world and the realm of the dead are the same location, which makes the creation account and the afterlife account share a floor. Neither reading can be excluded.
Does Niflheim have anything to do with the Nibelungs?
The resemblance between Nifl- and Nibelung has been noticed since the nineteenth century, and Wagner exploited it thoroughly — his Nibelungs are underground dwarfs in a place called Nibelheim, which merges the Norse mist-world with the German dynastic name. The Nibelungenlied's Nibelungs are a royal house and a hoard, not a location, and the philological connection between the two elements is disputed and probably false. Wagner's fusion is a magnificent piece of invention and it is not evidence about either tradition.