Which well is at the root of Yggdrasil in Niflheim?

The well at Yggdrasil’s root in Niflheim is Hvergelmir.

In Snorri Sturluson’s Prose Edda, Yggdrasil has three major roots extending into different regions. The root reaching Niflheim lies above Hvergelmir, an ancient spring associated with the dragon Níðhöggr, who gnaws at the tree’s roots.

Hvergelmir is not the same as Mímisbrunnr, the well connected with Mímir and wisdom, or Urðarbrunnr, the well beside which the Norns live. These three watery locations are tied to separate roots or parts of Yggdrasil’s cosmological structure.

The name Hvergelmir is also linked with the sources of numerous rivers in Norse mythology. It therefore represents more than a local pool: it is one of the primordial reservoirs underlying the mythic world. The detail comes chiefly from the Prose Edda’s account of Yggdrasil, while related references appear in the Poetic Edda.