Wording choices are evocative for the backstory. The wording could be tightened up a bit in a few sentences. You managed to dedicate an entire page to backstory. It's a bold choice, but due to how you did everything else, it worked well for you. I think the easiest improvement to the setup area would be finding a way to highlight or otherwise key-point elements that matter most. That way when I go to run this, I can just glance over it and immediately know what I need to jog my memory.
There's a limited amount of art here, but it's used well. Page one is evocative with the contrasting obelisks that aren't as they will literally appear, but instead placed to create impact. Very effective and immediately has me nodding about the choice. The other art is limited to maps, but I'm already fine with that. Making good use of what you have. Other layout elements are separating everything with rough wavy lines so there's no doubt about what goes where. Color is used effectively as well. The duality of the situation is reflected thematically in how you have the outer pages done in gradient and the inner pages contrasted. The thing that worked the least for me artistically is the division lines. The rest of the art elements felt so intentional that those lines felt like an afterthought. MSPaint sort of fuzzy digital lines. The single easiest improvement you can make on the art aspect is addressing the visuals of these lines.
Some playability suffers a few small issues. As an example, you have numbers for elements detailed about the map, but no corresponding number on the map. While the locations can be inferred, I don't want to be trying to do that mid-game. Adding a corresponding number on the map so you know where a bit is at a glance would go a long way. I can't really speak to stat elements for Cairn since I haven't played that system. That said, I didn't see anything that felt like it would raise a lot of eyebrows. Nothing broken as far as I can tell.
Thematically I would say this is certainly on point for feeling like something out of the Appendix N. The story behind it, the evocative language at the start, the visual impact of the image. Even the vague sense of naked people without actually showing true nudity that was so common on old book covers. Theme feels the strongest here out of everything about it.