Wow! Now this is how you do a non-Euclidean dungeon!
Well done. You've taken something very complicated and made it very understandable, even for an absent mind like mine. Making the blue faces wild Outer Planes is a great idea, and ties really well into the Danger Clock mechanic (itself a great mechanic, btw). It is a bit hard to judge -- I can't really hold in my head the way the dungeon would unfold. I feel like I need to print it out and play around with it to really appreciate the full scope of what you've done here.
Still, I don't need to playtest it or print it to know this is a first-class entry. The Visual Design is awesome, not just evocative, but usable and helpful to running the game. I really like the effect you've done with the highlights on the room headers, each one looks hand-drawn. I wouldn't have guessed you'd used Public Domain art; all three illustrations seem perfectly bespoke.
The writing is also excellent, enjoyable to read but clear enough to run. Thematically, I also think you've done a great job. This was a tricky prompt, and a lesser designer would have crumbled under it; you've grown some wonderful flowers on a hard patch of dirt.
I also like that this is a Capstone adventure. I'm a broken record at times, saying there should be more high-level content out there. As far the jam goes, however, I think it works against your Gameability a bit. Elements like the unmarked rooms or the Gallery of Vile Art would need quite a bit of prep work from a GM to really shine. Once the Jam is done, and these modules exist in their own contexts, I think those areas will add a lot of value, but it does weigh a bit against the pick-up-and-play element. All of this is, of course, balanced by the wonderful job you've done with the non-traditional map. Many GM's have tried to deliver on this idea, but I've rarely seen anyone execute on it in such a clear way. Other than the time cutting and pasting, even a beginner GM could navigate the complexity here basically without prep. Incredible.
All in all, this is a really fantastic adventure, definitely Winner's Circle material. Beyond that, I think it has a real chance to become a classic Shadowdark adventure. I can't wait to run it myself. Well done!
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Anyways, that's my top level/voting reaction. I know you're a fan of longer, more detailed reviews, with an eye to thorough constructive criticism, so I'll try to offer you some of that here. These are mostly matters of preference and minor quibbles; feel free to skip them if you're not in the mood.
- Some of the encounter balance seemed a little odd to me, perhaps partially because there's a big spread between the levels and numbers of PCs recommended. The party that can face 8 Stone Golems and live might not get a kick out of defeating 3d4 Rot Flowers.
- Along a similar line, there were a few places (5d6 zombies, 6d4 rat swarms, 6d6 spider swarms) where it seemed like fewer monsters of higher level might be more flavourful/impactful for the players and easier to run for the GM.
- Because Shadowdark is a treasure-as-xp game, a little more loot for the level 8 and 9 Crawlers might punch it up. Obviously, space is tight, but I think the copper coins in Room 11 (Treasure Pile) could be gold or maybe even reference one of the core book's treasure tables.
- In Room 4 (Horror Chamber), the tentacles could use an AC. Obviously space is at a premium, but I might be tempted to trade 'Grasping' for some more formatting (i.e. ATK +8 2d10 (near), that kind of thing).
- In Room 6 (Pool of Viscus Fluids), I think perhaps you meant to say 'Viscous Fluids'? Viscus (singular of viscera) does work, given the general flesh-wall-theme in this area, but I think you meant a thick fluid. Also in Room 6, you use a lowercase d in your dice notation (2d4, 1d3), while elsewhere you've used an uppercase D.
- This is user error, but by the time I got to Room 8 (Statue-lined Hall) I'd totally forgotten what Ohe Hano Ihu was. A (see cover) would've been good.
- It's a quibble, but in Room 13 (Gallery of Vile Art), I'd swap DM for GM. I think DM is proprietary? In any case, Shadowdark uses GM.
- In Room 14 (Library), I'd be tempted to remove the 1-in-6 chance of finding Haumea and Kaulu's history and just let Searchers find it. It adds so much to the adventure; why let 5-in-6 parties potentially miss it?
Anyways, I apologize if I've been overly particular here. I could make a much longer list of all the little victories in this module, but you strike me as the sort to prefer constructive criticism to flattery.
If I might venture one further critique: I was confused by your itchio username! I didn't realize you were DX Logan until I'd downloaded the module. My friend and I played Styx and Stones together a while back; I would have jumped to review this much earlier if I'd realized it was you.
Congratulations on your achievement here. I'm excited to see what you do next.