In order to understand the geography of the Nine Worlds, it is crucial to start with Yggdrasil, the World Tree. Conceptions of the World Tree have been found in tribal societies from Siberia to Polynesia; they differ in some aspects, but generally come with some kind of upper world in the top branches of the tree, some kind of ancestral world of the Dead at the roots, and various other worlds in the middle. It has been theorized that they are different trees on the same model, or that they are the same tree existing in many different dimensions, with different worlds in each, from my point of view and for what i have study, seen and understand, yggdrasil is a connection, a spiritual one, that leads us to an other realm, and other place / world, see it as a channel, and where you will jorney is a vast world/place where many diferent landscapes are, which to the ones who jorney there and travel, led them to belive that there are diferent worlds, but it is just one with so many “countries” and few dont have the chance to travel from one place to an other at the same time, they just “fall” in one and come back and then “fall” into an other diferent, it is like being in a countrie in Europe and then suddenly you are in a place in Africa and then again in an other place in North America, the landscape is diferent and it comes to the mind that it is diferent worlds, but with all the studying, you actualy can understand that there is connection from one place to an other by foot or sea. At least i can almost draw a map and we can see the connection by foot from Jötunheim to Muspelheim and from Jótunheim to Vanaheim by sea passing through isles.
Now back to the subject, we refer to the dimension of the Tree explored by the ancient Norse/Germanic/Saxon peoples as Yggdrasil. Ygg is a byname of Odin, and Yggdrasil means “Odin’s steed”, a kenning. This doesn’t mean that Odin owns or controls the Tree – he doesn’t – but he was hung on it once as part of a pain ordeal, and the reference is to him “riding” the tree in this way. The Tree itself is sentient, and has been known to send messages to people (and through them), but the messages are usually long, slow, and cryptic. The Tree is not a humanlike being, and its way of knowing and communicating is much longer and slower than ours.
Yggdrasil exists in a void of nothingness called Ginnungagap. Nine worlds spin around the tree – Asgard, Ljossalfheim, Vanaheim, Jotunheim, Midgard, Muspellheim, Svartalfheim/Nidavellir, Niflheim, and Helheim. As i have told before back there, these worlds are places, realms, landscapes, vast and great in the same place. The ancient Norse, not understanding the concept of a round world, or for that matter anything larger than their own small flat piece of Earth, told of them in the only ways that they could conceive of – as countries or continents on a flat plane. They spoke of moving between worlds as one would move from Germany to France (by crossing a river) or from Denmark to Britain (by crossing an ocean), many will disagree with me, but from what i have seen and study hard about this matter, the ancient people where not so far from the truth, the world is the same but with many many realms, it would be impossibel to one who did not die yet, to see it all and walk or swim in it from one place to an other, because that is not allowed, just in shamanic journeys and trance, you can “visit” a place and be there for a while and see it, but there is not enough time to make a great journey, it is just possible for those who have all the time of eternity.
Denizens: Yggdrasil is generally pictured as an ash tree, but this may be human interpretation. On the very top of the tree sits an eagle, Hraesvelg (“Corpse-Eater”), who is actually a wind-giant locked in eagle form. He is very old, of the first generation of Ymir’s kin. Winds – or rather, energy currents – blow from his wings, and are controlled by the wind-deer. At the bottom of the tree, crawling back and forth between Helheim and Yggdrasil’s exposed root in Niflheim, is the great dragon Nidhogg. She gnaws on Yggdrasil’s root, forcing it ever into new growth. Ratatosk, a squirrel-wight whose name means “Teeth That Find”, runs up and down the bark of the tree carrying messages (mostly insults) between Hraesvelg and Nidhogg. All three of them do not generally talk to most visitors and are not very approachable.
Four deer run through the upper branches. They are the keepers of the power of the Four winds, and are named Duneyr (Rest), Durathor (Slumber), Dvalin and Dain. Dvalin was once a Duergar, the son of the great Duergar leader Dvalin the Old. Dain was once an Alfar lord. Duneyr and Durathor were both mortals from Midgard. All four agreed to take on the forms of immortal deer and control the winds that blow from world to world.
This does not mean that they necessarily control the atmospheres of the various worlds. However, there are “winds” – currents of energy, really – that “blow” from world to world, and can sweep things and beings with them. Magically skilled folk can learn to “ride” these currents, but attempting to control them for one’s own purpose will bring one or more of the Wind Deer down upon you. While they do not engage in combat as such, their control of the winds means that they can sweep you quite literally off of Yggdrasil and into Ginnungagap.
The Guardians of the Four Directions are four Duergar known as Austri, Vestri, Sudri, and Nordri. Actually, it is unknown as to whether they are or ever were actually Duergar, or (more likely) whether they are divine entities who simply take on Duergar form. They are quite capable, and often do, take on other forms as well – elemental spirit-forms, birds, horses, dragons, etc. The Duergar of Nidavellir worship them as gods, and consider them to be divine entities who give the race of Duergar the honor of taking their forms. The four of them can be called on to help out if you have lost your way, as they know all the paths between worlds (and many within worlds) like the backs of their hands. They like to be invoked and poured for at gatherings and workings, but other wise do not require much in the way of offerings.