In Norse cosmology the World Tree Yggdrasil unifies the nine worlds that represent all that exists within the universe.
(Each of the nine worlds has a guardian on a threshold and a rune).
1. ASGARD, the world of the AESIR
ASGARD is the highest of the nine worlds, "enclosure of the gods." The warrior gods live here. It is the highest of the worlds and it's place above the horizontal plane shows it's separation from the other worlds. Odin rules over the world of Asgard. Colors associated with it are gold, silver and white. GIBO is the rune associated with this world. Heimdal is the guardian. He is the one you must deal with in order to enter the world of Asgard via the rainbow bridge. Midgard is located in the center showing the realm inhabited by humans.
2. LJOSSALFHEIM, the land of the light elves
LJOSSALFHEIM is characterized by the higher aspect of light and air. Humans interact with lower energies of the realms of the gods in this world. Colors associated with this world are yellow, light blue, light green and white. Inhabited by the light elves. Norse world of fertility. Delling an elf is the guardian and SUWOLO is it's rune.
3. JOTUNHEIM, Land of the Giants
JOTUNHEIM is frosty and rocky with violent winds and storms, located in the east. It is the turbulent world of elemental air which both breaks down and fertilizes. Colors associated with it are red and gray. World of Giants, the forces of chaos. Thrym the giant is the guardian and ISA is it's rune.
4. MUSPELLHEIM, the first world
MUSPELLHEIM along with NIFLHEIM is a world of ice and fire. It is set in the north on the outer limits of humanity due to it's destructiveness. The first world, the world of creative and destructive fire. The color associated with it is red. Surt the Destroyer is the guardian (he leads the evil force sent out for battle of Ragnarok) and DAGAZ is it's rune
5. MIDGARD, middle-earth, the realm of mankind
MIDGARD is the central world inhabited by humans, it's the world as we know it. It brings together all of the other worlds and is connected to them by roots, branches and the trunk of the tree YGGDRASIL. It represents the element of earth. The only realm subject to time. Midgard is the field of action where all the other worlds interact. Thor is the Guardian and JERA is the rune.
6. NIFLHEIM, the frosty Realm of Ice
NIFLHEIM along with MUSPELLHEIM is a world of ice and fire. It is set in the south on the outer limits of humanity due to it's destructiveness. Called the world of the dead. The color associated with it is black. The Nidhogg Dragon is it's guardian and NAUTHIZ is it's rune.
7. VANAHEIM, the world of the VANIR
VANAHEIM brings life from the winds of the west and represents the world of water. The colors associated with it are dark green, dark blue, brown and red gold. The Vanir gods live here in peace and plenty. Frey is the guardian on the threshold and INGUZ is it's rune.
8. SVARTAFHEIM, the domain of the dark elves
SVARTAFHEIM interpenetrates the subterranean regions of the earth. The mystery of earthly manifestations are found in this realm. Colors associated with it are dark brown, gray and red gold. World of the dark elves. They are greedy and over the creatures of the earth. Modsognir is the guardian and EIHWAZ is it's rune.
9. HELHEIM, HEL'S Domain of the Dead
HEL is the lowest of the nine worlds. It is the hidden root to which all things sink and rise, It is the dwelling of the dead. Colors associated with it are black, dark green and dark brown. Ruled over by Loki's daughter Hella. Hella is the guardian and HAGZLAZ is it's rune.