“The chief and most holy seat of the gods,” say the Eddas, “is by the Ash Yggdrasil. There the gods meet in council every day. It is the greatest and best of all trees. Its branches spread over the world and reach above heaven. Three roots sustain the tree and stand wide apart; one is with Asa; the second is with the Frost giants; the third reaches into Niflheim, and under it is Hvergelmar, where Nidhug gnaws the roots from below. But under the second root, which extends to the Frost giants, is the well of Mimir, wherein knowledge and wisdom are concealed. The third root of the Ash is in Heaven, and beneath it is the most sacred fountain of Urd. Here the gods have their doomstead. The Asa ride thither every day over the Bi-frost, which is also called Asa-bridge. There stands a beautiful hall near the fountain beneath the Ash. Out of it come three maids. These maids shape the lives of men, and we call them the Norns. On the boughs of the Ash sits an eagle, who knows many things. Between his eyes, sits the hawk, called Vedfolner. A squirrel, by name Ratatösk, springs up and down the tree and bears words of hate between the eagle and Nidhug. Four stags leap about in the branches of the Ash and bite the buds. The Norns that dwell by the fountain of Urd every day take water from the fountain, and clay that lies around the fountain, and sprinkle therewith the Ash, in order that its branches may not wither or decay.”
Source: The Prose or Younger Edda, translated by G. W. Dasent, p. 16