Yggrasil the World Tree by Holley Bakich
In Norse mythology, the great world ash Yggdrasil held up the universe. It grew out of the body of the great giant, Ymir. Its branches hold up the heavens, while its roots extend to the main three parts of the world: Jotunheim (the land of the frost giants); Asgard (where the gods dwell); and Niflheim (the underworld). Three wells nourish the tree's roots. The well in Asgard is guarded by the Norns (fates): Urda or Weird (past); Verdandi (present), and Skuld (future). The second well is guarded by the omniscient Mimir. The tree's third root is constantly gnawed by Nidhogg, a giant serpent, who will eventually chew all the way through at Ragnarok (the end of the world).