You've likely used the tag "indoors", and maybe even some related ones like "spacecraft interior". You've likely also noticed that when you do, there's an odd insistence of making windows be in the background because that has been so strongly associated with being "indoors". Luckily this is an easy fix: Just put "window" in your negative prompt.
A related issue is that "cave interior, underground" really likes to only partially be underground. "outdoors, sunlight" helps here too.
I felt this one was obvious, but figured I'd mention it anyways since they're negatives I use initially when prompting, rather than reactively when trying to improve/fix an image, and a lot of what I think is obvious turns out to not be.