What is "Asgard"? and other stuff you need to know

In Norse mythology, Asgard was one of the nine realms of existence. It was the highest realm in the Norse mythic universe and the homeland of the Aesir, the race of warrior
gods who were the dominant deities. The chief god was Odin Asgard was surrounded by a high stone wall that had been built by a stonemason called Blast. The vast plain of Idavoll was located at the center of Asgard.

This was the site of the inner hall of Gladsheim (Place of Joy), where the Aesir gods met in council. The hall of the goddesses, called Vingolf, was also within the walls of Asgard. Odin’s castle was the mighty Valhalla. This great hallwas where slain mortal heroes were brought to continue training and to wait for the coming of Ragnarok, the final battle, when they would fight on Odin’s side against the foe.

Bifrost was a rainbow bridge that linked Midgard, the realm of humans, with the gate of Asgard. It was made with magic and great skill by the Aesir and would stand until Ragnarok, when it was foretold that this rainbow bridge would collapse. At the entrance of Bifrost stood the god Heimdall, the guardian of Asgard. Heimdall’s hearing was so keen that he was able to hear grass growing on the mortal earth or wool growing on the back of a mortal sheep. Heimdall
also could see for a hundred miles.

The realms of Vanaheim and Alfheim also were found at this highest level of existence. Vanaheim was home to the Vanir, the secondary race of gods, many of whom intermarried with the Aesir. Alfheim was the domain of the lios alfar, the elf folk of light. The god Frey, said to be the father of the lios alfar, lived at Alfheim. Originally one of the Vanir, Frey was adopted into the Aesir pantheon and had his palace in Alfheim.