Yggdrasil

Yggdrasil is the immense ash tree at the centre of the Norse cosmos, whose roots and branches bind the nine worlds together. Its name is usually read as “Yggr's horse”, the steed of Odin, recalling the nine nights he hung on a windswept tree to win the runes, as Hávamál tells. Its three roots reach Urd's Well, where the Norns water it each day, Mimir's Well and the spring Hvergelmir in Niflheim. An eagle sits in its crown, the dragon Nidhogg gnaws it from below, the squirrel Ratatosk carries insults between them, and four stags graze its leaves. At Ragnarok the ancient tree shudders and groans, as Völuspá foretells.