This is the kind of adventure that would make Lovecraft feel like he's got to step up his weirdness game. Amazing vibes.
The spider note at the beginning is in hard to read text. I would probably trim text elsewhere -- you repeatedly give the referee permission to do whatever they want, for instance -- and bump up that font size and maybe pick a different font for the "handwritten" note.
The middle section of the adventure isn't as engaging as the set-up or the final encounter. I would be tempted to have the journey take less time and give the adventurers a weird small space to explore before the fight at the end.
Love the flavor of this. I can definitely see using this as a weird sidequest in all sorts of games.