Thanks for all of the input guys, but I finally figured it out while playing with a friend on his game. It was one of the stupid AN:BY pump stations! I didn't do that part, so I had no idea that one of them was actually underground.
I really wish these maps would change between floors so that you can see every aspect of it. Would make navigating through Sawtooth a whole lot easier. That, and give us some sort of way to keep track of these darn places, either a list or showing a name while scrolling on map.