Asgard

Asgard is the home realm of the Asgardians. It is ruled by Odin the Allfather; other notable inhabitants include Thor, Loki and Frigga. It is based on the Norse mythological world of the same name.

Asgard is a celestial planetoid in an unknown part of the Marvel Universe. It is not a planet like Earth or Jotunheim, but is instead a flat, mystical realm filled with cliffs and waterfalls that pour out space.

Trivia

 * It is stated in The Avengers that Thor was able to get back to Earth thanks to the powers of Odin; however, Loki commented that Odin would have had to "summon up" a lot of "dark energy." This suggests that this action may be tiring, and possibly even dangerous or frowned upon by Odin, and was likely why the Bifrost meant so much to the Asgardians.