Far future New York, year 3030. The sun has become a toxic mess, the ozone layer is broken, so we must stay underground. The world we know is a layer of metal sky, protecting us by the sun and storing solar energy to run the cities. There is projection technology that imitates night and day, and tunnels connect cities (towns are lost causes, and very few shoot off into each tunnel, usually bandits, smugglers, and crazies). Apartments are small and minimalistic, with a flow of technology that lives in the hub (truly Google headquarters). Food is vitamin-like at the most, flavorless—protein bars, nutrition drinks, chemically made stuff. The people are weaker than normal, but gyms are available but highly regulated to prevent excessive muscularity (resource regulation).
Those who can survive aboveground are contaminated and have a layer of plastic-like skin over their features, small inset eyes like a mole, and robust because they have true food. Plants can still survive, animals are dead, but cannibalism isn’t frowned upon Above.