In Norse mythology there are "nine worlds" (Níu Heimar in Old Norse), each joined to the other via the "World Tree" Yggdrasil. A list of these worlds can only be deduced from the limited sources given to us in the two eddas. A complete list of the nine worlds is never mentioned entirely, in either of the eddas.
A summary list of the worlds, with an example reference to where they are mentioned, either in the older Poetic or younger Prose Edda. (in no particular order) -
* Ásgarðr, world of the Æsir.
* Vanaheimr, world of the Vanir.
* Álfheimr, world of the Álfar (Elves).
* Miðgarðr, world of humans.
* Jötunheimr, world of the Jötnar (Giants).
* Niðavellir, world of the Dvergar (Dwarfs).
* Múspell, world of fire and the Fire Jötnar.
* Niflhel, world of ice and mist, into which the wicked dead are cast. / Niflheimr
* Hel, world of the inglorious dead, located within Niflhel/Niflheimr and ruled over by the giantess Hel.
Each world also had significant places within. Valhalla is Odin's hall located in Asgard. It was also home of the Einherjar, who were the souls of the greatest warriors. These warriors were selected by the Valkyries. The Einherjar would help defend the gods during Ragnarok.
These worlds are connected by Yggdrasil, the world tree, with Asgard at its top. Chewing at its roots in Niflheim is Nidhogg, a ferocious serpent or dragon. Asgard can be reached by Bifrost, a rainbow bridge guarded by Heimdall, a god who can see and hear for a hundred leagues.
Numerous beings exist in Norse mythology, including the Æsir and Vanir, two groups of gods, the Jötnar (Giants), the Álfar (Elves) and the Dvergar (Dwarves). The distinction between Æsir and Vanir is relative, for the two are said to have made peace, exchanged hostages and reigned together after the events of the Æsir–Vanir War.
In addition, there are many other beings: Fenrir the gigantic wolf, Jörmungandr the sea-serpent (or "worm") that is coiled around Midgard, and Hel, ruler of Helheim. These three monsters are described as the progeny of Loki. Other creatures include Huginn and Muninn (thought and memory, respectively), the two ravens who keep Odin, the chief god, apprised of what is happening on earth, since he gave an eye to the Well of Mimir in his quest for wisdom, Geri and Freki Odin's two wolves, Sleipnir, Loki's eight legged horse son belonging to Odin and Ratatoskr, the squirrel which scampers in the branches of Yggdrasil.
In the Poetic Edda poem Völuspá ("Prophecy [spá] of the völva"), Odin, the chief god of the Norse pantheon, has conjured up the spirit of a dead völva and commanded this spirit to reveal the past and the future. She is reluctant; she cries, "What do you ask of me? Why tempt me?" Since she is already dead, she shows no fear of Odin, and continually taunts him, "Well, would you know more?" But Odin insists: if he is to fulfill his function as king of the gods, he must possess all knowledge. Once the völva has revealed the secrets of past and future, she falls back into oblivion: "I sink now".
According to Norse myth, the beginning of life was fire and ice, with the existence of only two worlds: Muspelheim and Niflheim. When the warm air of Muspelheim hit the cold ice of Niflheim, the jötunn Ymir and the icy cow Audhumla were created. Ymir's foot bred a son and a man and a woman emerged from his armpits, making Ymir the progenitor of the Jötnar. Whilst Ymir slept, the intense heat from Muspelheim made him sweat, and he sweated out Surtr, a jötunn of fire. Later Ýmir woke and drank Auðhumla's milk. Whilst he drank, the cow Audhumbla licked on a salt stone. On the first day after this a man's hair appeared on the stone, on the second day a head and on the third day an entire man emerged from the stone. His name was Búri and with an unknown jötunn female he fathered Borr (Bor), the father of the three gods Odin, Vili and Ve.
When the gods felt strong enough they killed Ymir. His blood flooded the world and drowned all of the jötunn, except two. But jötnar grew again in numbers and soon there were as many as before Ymir's death. Then the gods created seven more worlds using Ymir's flesh for dirt, his blood for the Oceans, rivers and lakes, his bones for stone, his brain as the clouds, his skull for the heaven. Sparks from Muspelheim flew up and became stars.
One day when the gods were walking they found two tree trunks. They transformed them into the shape of humans. Odin gave them life, Vili gave them mind and Ve gave them the ability to hear, see, and speak. The gods named them Askur and Embla and built the kingdom of Middle-earth for them; and, to keep out the jötnar, the gods placed a gigantic fence made of Ymir's eyelashes around Middle-earth.
The völva goes on to describe Yggdrasill and three norns; Urður (Wyrd), Verðandi and Skuld. She then describes the war between the Æsir and Vanir and the murder of Baldur, Óðinn's (Odin) handsome son whom everyone but Loki loved. (The story is that everything in existence promised not to hurt him except mistletoe. Taking advantage of this weakness, Loki made a projectile of mistletoe and tricked Höður, Óðinn's (Odin) blind son and Baldur's brother, into using it to kill Baldur. Hel said she would revive him if everyone in the nine worlds wept. A female jötunn - Thokk, who may have been Loki in shape-shifted form - did not weep.) After that she turns her attention to the future.
Ragnarök refers to a series of major events, including a great battle foretold to ultimately result in the death of a number of major figures (including the gods Odin, Thor, Freyr, Heimdall, and the jötunn Loki), the occurrence of various natural disasters, and the subsequent submersion of the world in water. Afterwards, the world resurfaces anew and fertile, the surviving gods meet, and the world is repopulated by two human survivors.