There are nine realms in Norse Mythology, they are called Niflheim, Muspelheim, Asgard, Midgard, Jotunheim, Vanaheim, Alfheim, Svartalfheim, Helheim. The nine worlds in Norse mythology are held in the branches and roots of the world tree Yggdrasil. These realms are the home of different kinds of beings, such as Asgard the home of the Gods and Goddesses, or Jotumheim the home of the giants.

Valheim is a made up, topologically flat, realm that functions as Viking purgatory and may not be connected to the world tree or to the rainbow bridge (that may be why a huge raven flies you to Valheim) and the reason

that you die if you sail over the edge.