I’ve been on a cosmic horror kick lately, and what I’d really like to read is stories or novels of the awful and unfathomable on a spaceship. Stories where we go to them, poke what shouldn’t be poked, scan what shouldn’t be scanned, and things proceed from there.
I’m surprised, because there’s some obvious answers to this I don’t see here.
Blindsight A bunch of zombies, led by a vampire fly into deep interstellar space to rendezvous with an alien object that doesn’t understand or care about them.
The God Engines by John Scalzi. VERY different from Scalzi’s other work. FTL works because of psionic aliens who are horrifically tortured by priests to force them to warp space.
The Outside by Ada Hoffman. AI gods rule the universe and are horrific.
The Sollan Empire books by Christopher Ruocchio have MANY elements of this (and other SciFi tropes). The alien race at war with humans worship dark gods from outside the galaxy who want to destroy reality. They also consider humans to be an edible slave race and you’ll encounter the horrific things they do to humans right in book 1, but they really get into that in the most recent book.
Hyperion If the Shrike isn’t a form of cosmic horror, IDK what is.
Sphere by Michael Crichton. Ok, technically a submarine base, but there IS a space ship…