Top idea to avoid the obvious knight errant plot, making the hero into the prison of the beast is solid thinking.
Putting spacemen and knights together is a definite sci-fantasy trope, so absolutely appendix N.
Obviously if this was a movie, when the astronauts reach the inner sanctum, the viewers will also be muttering “don’t touch anything, just leave.” But in ttrpgs, as in movies, there’s always someone who thinks “what’s the worst that could happen…?” Answer- it’s an old school game, so the worst thing is usually pretty grim.
Really atmospheric and looks great to play