Behind the door is a long dark tunnel. Looking around to see if anyone can see you, you enter the tunnel and close the door behind you.
Creeping down the tunnel, you pass several wide doorways on both sides, but the growling noises warn you not to enter. You shouldn't be down here as it is.
You hear the sound of dripping water from an open doorway and peer in to see a large, mirky pool. further along, you what looks like heavy mechanical devices, including some sort of lifting gear.
Then you see light from around the corner. Peering round it, you find a large curtained doorway, leading outside to who knows where.