Vault of Life
The "Vault of Life", or more colliqually known as Level 0, is the deepest level of the city and is built entirely underground. It houses the vast majority of the city's critical systems, such as the fusion power plants, the enormous sewage systems, hydroponics plants, recycling facilities and atmosphere processors. In spite of its hopeful and bright name, Level 0 is dark, dreary and industrial. Several industrial production corporations have huge assembly and processing facilities housed here. The only light on Level 0 is the artificial glow of street lights, windows, neon signs and the occasional warm glow of an assembler. There is never any sunlight on level 0. It's dark, dreary, dirty, and the air is thick with smog.