If one took the Ministry lift to Level Nine, descended the stairs to Level Ten where the courtrooms were housed, and slipped into an old, empty broom cupboard, a hidden staircase could be uncovered that would take them down to Level Eleven completely off the official records. Hermione assumed that it was how the criminals in the past were brought up to the courtrooms for their trials. How it was lost to time was a complete mystery. She didn't mind much. In years of using it for her own purposes, she'd not once been caught.