Before their conversion to Christianity the Vikings believed the universe was comprised of nine worlds supported in the branches of the great world tree, Yggdrasil:
Midgard: the world of humanity
Asgard: the world of the Aesir, a tribe of deities led by Odin who control the forces of nature, also the home of the victorious dead, Valhalla.
Vanaheim: the world of the Vanir, another tribe of gods and goddesses
Jotunheim: the world of the giants
Niflheim: the primordial world of ice
Muspelheim: the primordial world of fire
Alfheim: the world of the elves
Svartalfheim: the world of the dwarves
Hel: the world of the eponymous goddess Hel and the Halls of the Dead.