Which isn’t exactly unexpected if you know your Norse mythology because Valhalla is in Asgard, so the clue was in the name the entire time. And you also know that Asgard is one of the nine realms of the world-tree Yggdrasil, so which other realms are in the game? Besides Midgard, obviously, but you know that too because it’s the realm of humans, including protagonist Eivor, and it’s kind of obligatory.
For now, you can also add Jötunheim, the realm of the jötnar, to the list.
Frequently translated into English as “giant”, the actual definition of a jötunn is ambiguous, and different from one source to the next – in the Eddas, for example, a jötunn could be a troll or a demon, and most of the gods of Asgard are themselves descendants of jötnar. Since the alfar are elves, the dvergar are dwarves, and the svartalfar can be elves or dwarves, assume that the jötnar are everything else because Norse mythology is complicated like that.
And in Assassin’s Creed Valhalla, the jötnar are probably giants, anyway.