In Norse mythology, the world tree, a sacred ash which spanned heaven and hell. It was evergreen and tended by the Norns, goddesses of past, present, and future.
Yggdrasil had three roots with a spring under each one: one root descended to the well Hvergelmir in Nifelheim or Hel, the realm of the dead; another ran to the well of Mimir, the source of all wisdom, under Jotunheim, land of the giants; and the third reached Urd's well under Asgard, home of the gods. Urd's well was a regular meeting place of the gods and was guarded by the Norns, who sprinkled the tree with its waters every day to avert decay.
Various creatures inhabited Yggdrasil, including an eagle and a hawk in the branches; four sacred harts who fed on the foliage; and Ratatosk, the strife-making squirrel, who travelled continuously up and down the trunk to maintain the hostility between the eagle above and Nidhogg, a dragon which gnawed ceaselessly at the root connecting to Nifelheim.