Asgard
Ruled By: Thor, King of Asgard
This is the home of the Norse Gods of the Marvel Universe. Asgard is a small extradimensional planetary body whose nature and physics are different from those of planetary bodies found in the Earthly dimension. The prevalence of magic entities it to be described as a mystic realm. Asgard is a relatively flat asteroid-like landmass floating in space. It has been described as floating on a "Sea of Space". This sea apparently has a surface, one that is navigable by Asgardian ships resembling Viking longships.
Asgardian cosmology recognizes "9 Worlds". These are probably the only worlds known to the Asgardians at the time they were worshipped by the Vikings of the Marvel Universe.
4 "worlds" exist on Asgard itself: Asgard, home of the gods (which includes Valhalla, a special region of Asgard containing the spirits of the honored dead); Vanaheim, home of the Asgardians' sister race, the Vanir; Nidavellir, the home of the Dwarfs; and Alfheim, home of the Light Elves.
In addition, Asgard is connected to different dimensions that contain the remainder of the 9 World's. Its main connection was to Earth (which the Asgardians call Midgard). This was reached by Bifrost, the Rainbow Bridge, which is now shattered in the middle. Passage to Earth is now difficult.
Jotunheim, the world of the Giants, is a flat ring-shaped realm with high mountains along its inner edge. It exists in its own pocket-dimension.
Svartalfheim, home of the Dark Elves, is another asteroid-like landmass that may or may not exist in its own pocket-dimension. There are numerous nexus-ports between the mountains of Jotunheim, Svartalfheim, and Asgard allowing easy passage between realms.
Hel is the realm of the those who died non-heroic deaths and Niffleheim its sister region, is the land of ice and home of the dishonored dead. Hel and Niffleheim both seem to have their own dimensional status, but are considered to be in the same "world" by the Asgardians.
The last of the Norse mythology "9 Worlds" is Muspelheim, land of the fiery daemons. All of these latter dimensions have interdimensional portals to Asgard, but are arranged in such a fashion that it seems as though they are "underground", or below Asgard.
There is a special passageway from Asgard to Olympus, home of the Greek Gods. Since Olympus is not part of the Asgardian cosmology, this nexus-port is most likely artificial rather than natural.
Beings of the Earth dimension have, in certain instances, been able to travel from Earth to Asgardian space. Asgardians themselves, particularly Thor and Loki, have taken an active part in Earth's affairs. Many magically enchanted characters or items are a direct result of Asgardian magic. While they do not reply as readily as many other entities, it is conceivable that Asgardian gods could be entreated for Dimensional energy with which to work spells.