Once I climbed down the ladder I stood in front of a metal door, this is the room behind that door. I think this is the room, and equipment that provided the electric power for the underground complex. Without a doubt this is the "backdoor" to this complex. The room itself was very damp and cold. It housed 3 rusted generators as well as what looked like a heating unit of some kind.
Working my way through the "generator room" there was a large empty room through a doorway to the left.
And to the right was another doorway to a room with two doors. Those openings led to two different areas. The doorway on the left led to several rooms while the one on the right led down a hallway.
I will post a map of this underground complex over the weekend.