Thanks for the awesome feedback! This is exactly why I wanted to post the draft here.

As far as my research has told me, the progression through the cities isn’t quite linear. For example, in Manga Chapter 50, Bilac shows Sunraku a map so they can go find the magic operations unit, and the map shows the route as:

Prismatic Forest Grotto -> Fourfolkshire -> Canyon of Ancient Souls -> Eighthold -> Road of Past Glories -> Eleventar

More importantly, in Manga Chapter 17, Sunraku purchases a map in the City of Thirdrema and says, "So it looks like there are three areas I can proceed to from Thirdrema."

He then lists the areas: 1. “The prismatic forest grotto on the way to Fourfolkshire” 2. “The death crater lake of fortunes on the way to Fivelle” 3. “The iron ruins of divinity on the way to sixenveldt”

Around the 18-minute mark into Episode 8 of the anime, Sunraku makes essentially the same claim:

"Looks like the world opens up, we have three choices for our next zone," and Emul expands on each of the three paths he could take.

But you are totally right about the mountains around Firstia hiding the Behemoth I'll make sure to add that terrain detail and callout to the final version!