Unofficially called the Undercity, more commonly called The Mines, beneath the city are networks of tunnels and underground complexes that house the lowest of the social classes. They evolved from old mining tunnels. Rumors say they connect to other cities.
The Mines are as their name suggests, a series a tunnels. They hold lines of tunnels which hold small one or two bot apartments. They some times reach into great caverns that houses thousands of apartments and shanty dwellings.
Under City is located directly beneath Vandorica City. It evolved from the mines first dug to gather resources for the newly arrived Vandorans and the Early Vandoricons. It the years that past as the mines were abandoned for asteroid mining, they became a refuge for the lowest of the social classes. As such it is the slums of the world.
There are rumors that gangs and other dwellers have taken to expanding the tunnels, leading to other cities.