Jotunheim is one of the nine worlds, the homeland of the frost giants and rock giants. Situated in Midgard, on the middle level of the Norse universe, Jotunheim is separated from Asgard by the river Iving, which never freezes over. It lies in the snowy regions on the outermost shores of the ocean. Mimir's well of wisdom is in Jotunheim, beneath the Midgard root of the ash tree Yggdrasil.

Jotunheim is ruled by Thrym ("uproar"), the feared king of the frost giants. The stronghold of Utgard, the chief city of Jotunheim and the abode of the giants, is ruled by the giant Utgard-Loki. Other strongholds include Gastropnir, home of the giantess Menglad, and Thrymheim ("house of uproar"), mountain stronghold of the giant Thiazi.

Source: the Encyclopedia Mythica, please visit their site for much more