In the Norse mythology, there is a tree of life called Yggdrasil. Its branches fanned over gods and men and giants and dwarfs. It sheltered all creation. It has three roots.
One root dug deep into Niflheim and under that root the spring Hvergelmir seethed and growled like water in a cauldron. Down there the dragon Nidhogg ripped apart corpses. Between mouthfuls, he sent the squirrel Ratatosk whisking up the trunk from deepest earth to heaven; it carried insults to the eagle who sat on the topmost bough, with a hawk perched on its brow. And Nidhogg was not content with corpses; he and his vile accomplices gnawed at the root of Yggdrasill itself, trying to loosen what was firm and put an end to the eternal. Other creatures, too, attacked and preyed off the living tree – four stags nibbled at the new leaves, and goats tugged and tore off the tendershoots. Parts of the huge trunk were peeling, parts were rotten. Yggdrasill whispered and Yggdrasill groaned.
A second root curled into Asgard. Under that root flowed the well of Urd, the spring of destiny, where the gods gathered each day and held a court of justice. The three Norns lived near by, Fate and Being and
Necessity. They shaped the life of each man from his first day to his last. And every day they sprinkled water on the branches of Yggdrasill and nourished the suffering tree.
The third root burrowed into that part of Jotunheim held by the frost giants. Under that root bubbled the spring guarded by wise Mimir, and the water in that well gave insight to those who tasted it. But one has to pay a price to taste that water. The god Heimdall left his shrieking horn there until the day when he would need it to summon every living creature to Ragnarok. And God Odin had given one eye for a single draught from it. He won immense knowledge there and with it the thirst for yet greater wisdom. So the Terrible One-Odin-approached Yggdrasill alone.