The datapad proves to be a little bit more complex then you originally thought. It describes a route down to the surface using a series of maintenance tunnels and elevators that were used back when the city was first being built upwards then went into disuse afterwards. That left a somewhat crooked and broken path downwards if you followed it properly. There were other ways down, but the surface was a sort of no mans land that had only the original elevators left downward. All of which required an access code. The datapad mentions a few groups that would have the code, a few gangs, the exchange and a few corporations that had in the past looked for rare minerals beneath the surface.