Jötunheimr (or Jotunheim) is the land of the giants in the Norse mythology. Two kinds of giants (or Jotuns) live in Jötunheimr, rock giants and frost giants. From here they can attack the humans in Midgard and the gods in Asgard. Jotunheim is ruled by King Thrym.
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Jotunheim Facts for Kids. Kiddle Encyclopedia.