At that time, the so-called "abandoned people" who were left on the earth had been living in the underground city for so many years that they had forgotten the blue sky and the bright stars. Because the ground has already become uninhabitable due to thermonuclear pollution. In the early years, real estate in underground cities was penniless, and every inch of land was as valuable as paper in Luoyang. Survival was the greatest significance in the post-war era.
The underground city is generally divided into three layers, which are the sky city on the top layer, the underground palace in the middle, and the lower realm on the bottom layer. The most vast sky city is the political, economic, cultural and educational center and the gathering place of the powerful, with the best materials, energy and the most livable climate; the underground palace, which is less than half the space of the sky city, supports most of the earth's survivors. There are commercial areas, logistics areas and relatively large civilian areas; the worst living conditions are in the lower realm called "region", where there are mines, factories, energy collection and conversion bases, data centers and some slums.
The three major floors of the underground city are independent of each other, but also a whole, because the urban temperature control, ventilation, water supply, drainage, solid waste treatment and other life-support systems are mutually restrictive. As the underground city was perfected over time, humans who survived the thermonuclear war gradually accepted and adapted to a life without seeing the light of day.
Purpose: Survival is the first priority of all civilizations