Norse Cosmology - The Nine Realms
According to the Nordic poem Edda, there is the existence of nine worlds, but they are not explicitly listed. It was only through a review of the Nordic literature was a tentative list of all nine created. They are held and supported by the World Tree, Yggdrasil, although no text explicitly describes how the realms are arranged on or around the tree. The nine worlds are.
Midgard, the world of humanity
Asgard, the world of the Aesir tribe of gods and goddesses
Vanaheim, the world of the Vanir 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
Nidavellir, the world of the dwarves
Hel, the world of the eponymous goddess Hel and the dead
Apart from Midgard, all of the nine realms are almost completely invisible to the naked eye. There are some exceptions however, where certain realms become slightly visible from certain parts of Midgard. For example, Hel may become semi-visible from graveyards, Asgard with the sky, and Jotunheim from the wilderness.