Yo. I'm helping my lil sister to brainstorm ideas for a novel since we just got a shit ton of money from an inheritance and one of her dreams was writing a novel and getting some japanese old lady to draw a manga off it.

basically I'm looking for books involving "shell worlds", like Matryoshka doll style planets that have different layers, mostly to find out what could work better as a source of artificial light and day/night skies.

she wants to make 5 layers are each planet-size for her novel, so if she ends up liking the universe, she might write more about it in the future. obviously everything is still in Drafts and she's changing a lot regarding the plot. But making a "shell world" work is what she wants to figure out right now.