I want some kind of "space habitat simulator" where I can see what it would look like to be on a ringworld, or a Culture orbital, or other sci-fi habitats (a spindle? Dyson sphere?)

Something like Elite Dangerous so you can fly around it or visit the surface. (ED has rotating asteroid parking garages, maybe you can walk around them by now.)

Just something with realistic (!) scale, lighting, atmospheric effects etc., rather than just an arch painted across a skybox.