Jötunheim is the third world inhabited by Giants, the other two being Muspelheim and Niflheim. There are many different words used in Old Norse to describe members of the “Giant tribe” but “Jötunn” is by far the most common one. We have no lore as to how Jötunheim came into existence but we still know a few things about how the Germanic Peoples imagined the place to look. In Skirnismal the poet tells us that Jötunheim is protected by a wall of flames. Behind the wall the heartland is additionally protected by a barren mountain range but once these obstacles are overcome, the sight that greets the eye is quite mundane. There are halls, fields, gardens, dogs and cattle. Aside from the areas inhabited by Jötun-families it seems to be a wild country full of mountains and deep valleys, with large areas covered in dense woods populated by wildlife. The sources do not tell us much more about its landscape but the most fascinating aspect of Jötunheim are its inhabitants.
The Giants are very present throughout the sources but that doesn’t really make it any easier to characterize them. One myth we can check at the door is the idea that all Giants were incredibly tall as this is a feature that they only acquire later on when the Myths turn into folklore and fairytales. Some of them are really strong and tall but in the Norse sources this is not a prerequisite in order to be called a Jötun. Some of them are really ugly like Tyr’s grandmother that we encounter in Hymiskvida who is said to sport 900 heads but then Frey’s wife Gerd, who is also a Giantess, is said to be so beautiful, that her future husband immediately falls head over heels for her at first sight. The same goes for their character and their relationship with the Gods. It would be wrong to declare the Giants to be evil by default, it seems that they are actually a similar tribe that tries to stage a coup from time to time in order to gain the upper hand in the war for dominion over the Universe. Two of the most famous power grabs were initiated by Thrym (Thrymskvida) and Thjazi (Skaldskaparmal 2-4).
Thrym was a king amongst the Giants and one night managed to sneak into Asgard where he grabbed Thor’s hammer. Since Thor is the one that keeps the Giants at bay by using Mjölnir (the hammer that Thrym stole) the reign of the Gods was truly threatened by that. Thrym agreed to return it in exchange for Freya’s hand in marriage but she wasn’t having it and so the Gods had to revert to trickery in order to get it back. Part of their ruse was to put Thor into a wedding dress so best go and read the story for yourself.
Thjazi was another powerful Giant, maybe even a descendant of Thrym as he is said to live in Thrymheim (Grimnismal 11, Gylfaginning 23). He managed to force Loki to lure Idunn out of Asgard where he abducted her. This was a real danger for the Gods as well because Idunn was the guardian of the apples the Gods had to eat in order to stay young. They managed to get her back but killed Thjazi during her rescue. This almost proved to be fatal as Thjazi’s equally powerful daughter Skadi showed up in Asgard, looking for revenge. In order to avoid disaster, they offered her to marry one of them and from there on out she is counted among the Gods.
The story of Skadi shows that the Giants and the Gods were in fact not so different and should be seen more as two warring tribes than two completely different species. The difference between the two tribes and the reason why the Giants are incapable of overcoming the Gods seems to be connected to consciousness. The Giants oftentimes steal objects of power from the Gods like Thor’s hammer or Idunn’s apples (including Idunn herself) but they seem incapable of actually using the loot. This becomes most obvious in the story about the mead of poetry (Havamal 104-110, Skaldskaparmal 5-6) where Suttung, another powerful Giant, comes into possession of said mead which is the source for wisdom, knowledge and poetry in the world. Through trickery Odin manages to get it back but instead of using the mead, Suttung has locked it away beneath a mountain where his daughter has to guard it day and night.