Jotunheim is the realm of giants in Norse mythology. After the gods had killed Ymir, the blood that poured out of his body had caused a flood. All giants drowned as a result, except for two. These were Bergelmir, who is a grandson of Ymir, and his wife. After floating around for days the two of them finally make land in Jotunheim, where they start the repopulation of the race of giants.
Jotunheim is frequently mentioned in Norse mythology. To protect Midgard and Asgard from the growing population of giants, the gods used the eyelashes of Ymir to shield off these realms from any giants’ invasions. Despite these protective layers, both gods and giants are known to cross the borders from time to time.
Thor and Loki would frequently travel to Jotunheim, usually ending up in some sort of quarrel with the giants.