extensive use of check (as opposed to description) cripple and otherway smart, creative adventure, whichemake good use of the prompt. With this amount of words and this raw imaginative power one could have been doing a top notch work. Very good anyway, could play

i think this is a creative use of the title and a solid premise. Eaten by a giant monster/being inside larger creature is a time-honored trope that gives you a lot to work with. I think the shrimp people are fun and funny. Are they parasitic/symbiotic with the Zetafish? RT1 should have more detail about what the players could interact with. Describe some aspects of the Zetafish so GMs have something to work with. How is it different than other space whales we've seen in other media?

I would advise against calling rooms "boring". You've got total control here. Don't make things boring, make them interesting. If there's nothing to do, there should be something to learn. Maybe the villi/phalanges have evidence of other things the zetafish ate. Maybe there's loot there. Maybe there's evidence of some high tech/magic species the PCs have been looking for. I don't know, but don't call stuff boring.

This has the structure of a fun, unexpected adventure. I wish there were more details on the Zetafish ecology and what we find there, and less mechanics and GM asides. I think you're almost there.

The dungeon inside a monster is a very good idea, and it seems pretty playable in one session.
I have some issues with the writing :
* outlining monsters or objects in bold or italics helps me as a GM in my session prep
* I think the room descriptions can be shorter and so we would have a little more info for the prep
* And I'd like more info on the Zeta fish, and which statblock to use for the shrimp people.
I think for lvl 1 or 2, DC 15 checks are a little hard if they are supposed to be succeeded for the most.
Great job anyway, I will use some of these ideas if my PCs are stock in a big Astral Sea monster.

The layout is nicely done. You've done a great job at separating information into clearly delineated blocks. 

You mention that this adventure is for level 1 or 2 characters, but for what system? The capabilities of level 1 creatures are very different between rule sets. 

You hit the theme really well, not sure what's weirder than being burped up by a giant space fish. 

I think this adventure was awesome, trying to be alive inside a giant creature? That aside, there are some things that I have to question:

• I think generally, your job is to make the rooms interesting (or at least help the GM with that), so that players are rewarded for adventuring. Because if not, can't they just go up from the way they come before? I think the lines of "Don't linger on this room, it's boring", or "Nothing is keeping the adventures in this room, they can move at any time" feels reductive.
• The mechanic for RT1 is interesting, but personally this would've been better if it was gimmick for the whole belly. There's a recurring theme and players can be vigilant on which checks they should do throughout their descend.
• I do appreciate you encouraging the GM to create facts about the zetafish, but without not many information to begin with, I feel like it's just...hard for the GMs to do that. A rumour table or an information table could be nice to help GMs answer the questions about zetafish itself.

A little random encounters could help making the adventure more spicier, the only way I can see myself running this adventure would be to deliberately speedrun it. If that's your angle for minimal prep, then that's good. Anyhow, it's still a worthwhile entry, good job!

It seems like you made this dungeon for D&D 5e, given the monsters and DCs,  in which case you should probably make that clear so your audience knows how to run it. I also like to put page references to where creatures can found in the core books so it is easier to GM. I also question inculding the philanges room  (RT4)  given that you yourself call it boring. It might be more interesting if someone/something was trapped inside so they would have a motivation to try and get them out.
I do like how fleashy all the description are, very fitting for the dungeon crawl inside of a monster! 

Love dungeons that are inside giant monsters!