Yggdrasil (Old Norse: Yggdrasill) is the name of the immense cosmic tree that serves as the connection between the Nine Worlds in Norse mythology. Known as the World Tree, Yggdrasil was said to lie at the very center of the universe, supported by three roots which extend far away into varying locations. Various creatures dwell within Yggdrasil. Upon the onset of Ragnarök, Yggdrasil will shudder and groan, ultimately crumbling as the universe meets its end.
Yggdrasil and Its Structure change
Yggdrasil's roots extend into three locations: Urðarbrunnr (Old Norse: “Well of Urðr”), Hvergelmir (Old Norse: “bubbling" or "boiling spring"), and Mímisbrunnr (Old Norse: “Well of Mímir"). As seen in the Poetic Edda poem, Grímnismál (Old Norse: "Sayings of Grímnir"), various creatures dwell within the World Tree, including:
Níðhöggr (Old Norse: Níðhǫggr - “Malice striker”), a massive dragon/serpent-like being that gnaws at its root(s), an unnamed eagle, and the hawk Veðrfölnir (Old Norse: “wind bleached” or “wind-witherer”), who sits between its eyes, along with the four stags Dáinn, Dvalinn, Duneyrr, and Duraþrór.
The Three Norns (Old Norse: Nornir) - Urðr (Old Norse: “fate”), Verðandi (Old Norse: possibly “happening” or “present”), and Skuld (Old Norse: possibly “debt” or “future”) - attend to Yggdrasil, weaving the fates of both gods and men.