Reading Jotunheim as the enemy country is the standard mistake. The jotnar are older than the gods and the gods are largely descended from them. Odin's mother is a giantess. Thor's mother is Jord, and the mother of his sons is the giantess Jarnsaxa. Loki is a giant by birth and lives among the Aesir as Odin's sworn brother. Freyr gives away his sword to marry the giantess Gerd, and that missing sword is why he dies at the end.
What separates the two groups is not species but position. The gods hold the enclosed centre and the jotnar hold everything outside it, and the traffic between them runs constantly in both directions: marriages, thefts, contests, insults and visits. Thor kills giants for a living and is himself half one.
The word is usually translated giant, which imports size and stupidity that the sources do not consistently supply. Some jotnar are enormous. Others are beautiful, several are wise, and Mimir, whose counsel Odin needs, is one of them. A better sense is an older order of beings whose claim on the world predates the gods' claim, which is why the eschatology has them taking it back.
The eschatology follows from the arrangement. When the world ends it is the jotnar who bring it down, led by Loki, who has lived inside the walls for the whole story. An enemy who is also kin, also a guest, and also the one who solves the gods' problems for them is a considerably more uncomfortable figure than an outside threat, and the sources never resolve him into one or the other.