The Stygian Library by Emmy Allen is an adventure of sorts. There's certainly an argument that it's not, and it's a convincing argument that I largely agree with. I'd rather consider it an adventure generator, with adventure in this case referring to a dungeon type adventure.
The setup is that there exists a kind of extradimensional space in which exists a kind of weird library full of all the knowledge in the universe. Getting there requires a lot of books in one spot, be large enough to have unseen areas, and have someone die there. At which point a door will appear which will grant access.
The gimmick is one the the Author has used in another adventure of theirs, The Gardens of Ynn. That gimmick is that there is no predefined location, but rather the place is intended to be generated during play with random tables. This is why I buy into the argment of it being an adventure generator rather than an adventure in itself. It runs as a pointcrawl rather than a traditional dungeon crawl, with new areas being spawned off of existing ones if you venture forth from them. To generate an area you roll a location table which describes the scenery, a details table to give extra goodies, and a random events table to shake things up. The GM then quickly turns those prompts into something usable. The logic behind this is that it's reusable, captures the feeling of a strange extradimensional space, and preserves the exploratory feeling for the GM as well as the players. The 'depth' of the party, or distance from the entrance is added to rolls, making the weirder stuff only show up deeper in the library while the more benign is close to the entrance. There's also a progress mechanic which tracks the search for whatever information you're looking for in the stacks.
The author rightfully recommends reading the book a couple of times before even trying to run it, and that makes a lot of sense. I've used books with investments like this in the past and they can be really excellent. That said, for a single adventure site, it feels like a lot of work. Especially compared to something like The Night Wolf Inn by Anthony Huso which is not only an adventure site in itself, but can act as a fun base camp of sorts for further adventuring.
The stuff that is in the book though is really cool. I'm familiar with the author's style since we've talked quite a bit over the years on the internet. This one facet of their work really appeals to me, and that is this sort of weird, abstract and mildly unsettling/creepy whimsy that is dark without being overt or edgy about it.
Presentation wise, it's knocked it out of the park. The book is beautifully made, as expected of Soul Muppet. The black cover with silver foil writing and cover picture is striking to look at. Inside, the text is large, bold and clear. The paper is thick with a textured feeling, feeling very high quality, it's all in a pale grey which makes it easy on the eyes too. The art is very stylised and stark black+white. It captures the feeling excellently. It's laid out in an very usable way while remaining visually distinct, which I can very much get behind.
It's certainly interesting to look at and I'm glad to have backed it. Is it something that I can see myself using? Yes. Perhaps not the intended way, but rolling ahead of time for the sake of having better notes and such, with more interesting traps and treasure seems like something I can put to work.
Don't think I've got the words left for the mini dungeons. In a word, they're fine. Okay little pickup games for when you've got nothing else and need something for a one-shot. Shouldn't be compared to proper dungeons though.