From Introduction:
The Norse gods are divided into two major groups, the Aesir and Vanir, in addition to the giants who came before them. Some believe the Vanir gods represent an older pantheon of the indigenous people whom the invading Aesir encountered. After a millennia long war, both sides agreed to an exchange of three gods who would live with the other tribe to further peace between them. While the three Vanir who came to live with the Aesir are Njord, Frey and Freya, nothing is known of the three Aesir who went to the Vanir. It is believed that in the end, the Aesir, eventually overcame and assimilated the Vanir.
The cosmology of Norse mythology places the earth, known as Midgard and is a circular disk, in the center of a concentric circle surrounded by sea. Across the sea is the home of the giants, Jotunheim, also known as Utgard. The gods’ home lies above Midgard in Asgard, which is connected by the rainbow bridge, Bifrost, which also connects to the World Tree, Yggdrasil. Hel lies below Midgard in Niflheim. After Odin created Midgard, he built Asgard, the home of the gods. There were many halls in Asgard for all the gods, some of which are
named below.