What the other districts don't know is that the residents of District 13 were not all annihilated during the bombing those many years ago, some survived by retreating to it's underground sanctuary. It is deep under the earth with ever-expanding apartment-like living quarters. They're always rationing food and high on security down here. They have a large cafateria, exercise room and an emergency War Room. The ammunition/weapon and high command rooms need finger and eye scanner identification. The lowest level is the prison cells, where any possible spies are kept for questions (and perhaps even torture means).