The poems use Niflhel, misty Hel, for a place low down and cold. Snorri uses Niflheim and gives it a much larger role, placing it in the north of the void before creation and making it the source of the eleven rivers that flow from the spring Hvergelmir. Modern retellings follow Snorri, because he is the only source that offers a system, and the system is very likely his.
That is worth stating whenever this cosmology is described. The Prose Edda is a thirteenth century Icelandic handbook written to teach poets the old references, by a Christian, two centuries after the conversion, and it is organised, coherent and readable in a way the poems are not. Its coherence is an achievement of composition, not a report of a doctrine, and where it is neat the poems are usually not.
What survives of Niflheim outside Snorri is a direction and a quality: down, north, cold, wet, and where the dead who are not chosen end up. Nidhogg is at its root gnawing. The rivers run from it. It has no ruler of its own, no hall, and no incident attached to it, which is unusual in a corpus that is otherwise made almost entirely of incident.
Naming it is still worth doing. A cosmology needs a cold pole as much as it needs a hot one, and the account of creation from the meeting of ice and fire does not work without both. Niflheim is a structural requirement of the story rather than a location anybody expected to visit, which is a reasonable description of quite a few places in this catalogue.