I'm having a mental blank with this and am hoping you can help me brainstorm more ideas. My current project is post-apocalypse, with some people living underground. I have one community that is in caves with no natural light available. Obviously they can't just get around in the dark, so where do they get light? The area they live is cavernous, so there would need to be a lot of light, not just torches. The other issue is vitamin D - though I'm considering bending the truth on that detail. The community is about 1000 people and has been established for at least one generation. Ideas? I have a few up my sleeve, but not entirely happy with any of them yet (mostly because of the vitamin D issue).