Go down the elevator in the centre of the main room. In the basement, there are blocks attached to the walls. You can push and pull them, to spin the walls of the room around. Spin the walls of the basement to find 3 switches. Once you have pushed all of the switches, spin the walls so there is a clear path to the boss room.
You may need to find one switch before another, as bar doors block at least one of the switch rooms (if my memory serves me correctly!)