According to the Norse poem The Lay of Grimnir, “Of all trees, Yggdrasil is the best.” Yggdrasil is a huge ash tree that stands at the center of the cosmos, protecting and nourishing the worlds. The gods are described as riding out each day “from Yggdrasil” to deal out fates to mankind, and it was on Yggdrasil that the supreme god Odin willingly sacrificed himself, hanging in torment for nine long nights before he could seize the runes of power. Yggdrasil supported nine worlds, set in three layers. At the top was Asgard, the realm of the Aesir, or warrior gods, Vanaheim, the realm of the Vanir, or fertility gods, and Aflheim, the realm of the light elves. In the middle, linked to Asgard by the rainbow bridge Bifrost, was Midgard (Middle Earth), the realm of mortal men, and also Jotunheim, the world of the giants, Nidavellir, the home of the dwarfs, and Svartalfheim, the land of the dark elves. Below was Niflheim, the realm of the dead, and its citadel Hel. The ninth world is sometimes said to be Hel and sometimes the primeval fire of Muspell, which will devour creation at the end of time. Yggdrasil itself will survive, and will protect in Hoddmimir’s Wood the man and woman who will re-people the world. The branches of Yggdrasil spread out over the whole world, and reach up to heaven.