User blog comment:Inept Wiki User/Cosmos in the Lostbelt: Post-Prologue, Pre-Anastasia Information & Speculation/@comment-25431873-20180806151059

We got some infos on Lostbelt #5 from the Norsebelt chapter. Confirmation comes from [the currently translated bits of Norsebelt] on Reddit, there is [this post] on Beast Lair and [this other post] providing the texts in the original Japanese, mainly from conversations with Caenis.

It's definitely Greece, as implied by both Da Vinci and Kotomine:

Da Vinci: The wall of storms are only covering the Scandinavian Peninsula. It doesn’t look like there’s anything coming from Greece’s side. And uh……well I didn’t want to add any unnecessary anxiety but, we can’t observe Britain. The Border can’t monitor what’s going on in Britain with its current equipment. We’ll need a much larger eye for that.

(this also confirms Lostbelt 6 being Britain/Camelot, but this probably isn't a huge surprise)

Priest: Of course, it did stop. If I hadn’t done so, did you think Mr Holmes would let us so easily escape? If he realized that you were alive, he will surely come back for you. That would put me in a difficult spot. Kirschtaria, has instructed me to bring you to Olympus.

From the other sources, Zeus might be the King of that Lostbelt, there is some trouble with Poseidon and Artemis, and apparently the Lostbelt's Tree "Atlas" is larger than all other Trees and cover 80% of the Earth's surface.

Interesting stuff all around.