In Norse religion, Asgard is one of the Nine Worlds and home to the Aesir Gods, Slain Warriors and the Aesir Goddesses. Located on the highest level of the Norse universe (Yggdrasil), it is surrounded by a high wall of closely fitted stone blocks. One of Asgard's well known halls is Valhalla, an immense hall where warriors died in battle await Ragnarok (kind of a Norse Heaven).
Each important God had his/her own palace in Asgard, such as Thrudheim, the realm of Thor or Breidablik, the home of Balder. There was only one entrance to Asgard, known as Bifrost or "Rainbow Bridge", which was guarded by the God Heimdall. Heimdall sleeps lighter than a bird, sees one hundred travel-days in each direction, and has such sharp ears that he can hear the grass and the wool grow. But as strong as Bifrost is, it will collapse when the when the Giants ride out over it at Ragnarok.
Many stories in Norse mythology happened in Asgard but for those who work in the construction business. The walls surrounding Asgard were built by Hrimthurs, who asked in payment the hand of Goddess Freya plus the Sun and the Moon. God Odin agreed providing the walls be complete in six months. Hrimthurs had a magic horse, named Svadilfari, who helped him in his work. To the Gods dismay, with but a few days left, Hrimthurs was almost finished. God Loki, the trickster, turned himself into a mare and charmed the stallion Svadilfari away. The job was not completed in time and no payment was given.
Valhalla, Hall of the Slain, in Norse mythology is the hall presided over by Odin. When Heimdall sounds his horn, the slain warriors and Gods will join the final conflict. The Norse myths held that Asgard would be destroyed at Ragnarok, the final battle in which the Giants would overcome the Gods.
Asgard is a fictional realm within the Marvel Comics universe based on the Asgard of Norse mythology and is home to the Asgardians and other beings of Norse mythology. Asgard features prominently in stories that follow Marvel's super heroic adaptation of the Norse God Thor.
I honor the high world of Asgard,
and the Aesir who offer knowledge and power.
So may it be.