Looking at the nine main realms is really all there is to it, since norse mythology keeps things pretty set in stone with midgard asgard vanaheim and the rest. While you won't find any secret tenth realm hiding away, there's actually quite a bit of interesting stuff tucked into corners of the existing ones. The forbidden sands section in alfheim, for example, has some really tricky environmental puzzles worth checking out.

If you're hunting for hidden areas, keep an eye out for spots that seem suspiciously empty or paths that look like they lead somewhere interesting. Places like baldur's dragon remains in midgard's ice walls need the draupnir spear to access, and there are some cool chambers connected to yggdrasil's roots scattered around. The realm between realms is technically its own space for fast travel, but it's more of a pathway than a proper realm.

Tip: those collectible rune inscriptions and tablets you find actually tell you quite a bit about how the realms connect, even if they don't reveal any new ones. The vertical exploration in each realm usually leads to good stuff like legendary chests or berserker fights, so it's worth thoroughly checking around.