Asgard (Old Norse Ásgarðr "home of the Aesir") is the dwelling place of the deity of the Aesir according to both the Edda of Snorri Sturluson and the Song Edda. Asgard is located in the crown of the world ash tree Yggdrasil and is connected to Midgard via the rainbow bridge Bifröst.
Asgard is described in the Grimnismál, the second song of the gods in the Song-Edda, as a huge castle. This consists of the twelve palaces of the gods and is surrounded by impregnable walls.
The twelve sky castles are made of gold and precious stones, the lattices of the palaces of golden spears; walls and floors are paneled in gold, on the ceilings hang the radiant shields of the heroes.
Valhalla and Sessrumnir are mentioned as the largest halls, where the heroes gather after their death. From his throne Hlidskialf the supreme god Odin can overlook all nine worlds.
The gods of the Vanir race, on the other hand, live in Vanaheim, which is also part of "Heaven" in most depictions, but lies outside Asgard, as does Álfheim, the home of the Elves. Rarely, Asgard is also depicted as part of Midgard.
"In the north of the mountains, which surround the whole inhabited land, a stream falls through Swithjod, which is rightly called Tanais; it was formerly called Tanaquisl or Wanaquisl; it flows out into the Black Sea.
The land between the arms of the Wanaquisl was then called Vanaland or Vanaheim; the river separates the three parts of the earth; the one to the east is called Asia, but the one to the west is called Europe.
The land to the east of the Tanaquisl in Asia was called Asaland or Asaheim; but the main castle which was in the land they called Asgard." (Heimskringla)
The gods had Asgard's walls built by a giant who was to receive as a reward the goddess Freya as his wife, as well as the sun and the moon. On Loki's advice, the gods set him a deadline.
He was to complete the entire construction in only six months, without any help. The Mature Giant accepted the conditions, but insisted on being allowed to use his horse Svadilfari.
Uncertain at first, but encouraged by Loki that even a horse could not help the builder complete the work in time, the gods accepted the terms.
To the gods' dismay, however, it seemed that the builder would be able to keep his end of the bargain - three days before the deadline, all that was missing was an archway.
The horse Svadilfari brought mighty stones during the night. Loki then turned into a mare, seduced the stallion Svadilfari and thus stopped him from working. As a result, the deadline was not met.
Loki gave birth to Odin's stallion Sleipnir as a mare. Enraged by the cunning of the gods, the builder revealed himself as Hrimthurse, who were enemies with the gods, and was slain by Thor with his hammer Mjölnir.