I’m currently thinking about how I would create an interior world. I think it would be pretty awesome to be able to see thousands of miles off in the distance. Imagine seeing the lights of Chinese cities from Europe at night. I suppose creating it would involve similar techniques to creating a planet but inverting the heightmap so mountains appear on the interior.
Any advice or theory that could help me in my endeavour?
You might want to consider using WM or other terrain creation tools as normal, then applying the resulting maps and textures to the inside of a sphere in a more general modeling application. In other words, don’t try generate upside-side down moutains. Generate everything right-side up and place some of it on “the ceiling”.
Also, not sure how much reality you are going for, but the Earth is just under 8,000 miles in diameter. Almost all the air is within 20 miles of the surface. If the interior of your world is filled with air at atmospheric pressure, you’re not going to see the lights of Interior China through 8,000 miles of air very well. That’s 400 times as thick as what an astronaut orbiting Earth has to look through.
It’s actually a fantasy world, I was just using Earth as an example. If the only source of light was an interior sun and there was no night then yeah you probably couldn’t see much at all from the sunlight scattering in the atmosphere. Probably couldn’t see China from Europe but maybe from North and South America…