As Miko readied herself, and Leroy opened the door, the hum of engines became stronger. Inside, there was a walkway, fastened to the left wall of a larger room, about 3 meters above ground level. Down there, big machinery still worked, probably on keeping the water clean and the supplies full in the building. A mass of pipes crossed the floor, sometimes one, sometimes a group, steel ladders crossed those at places. A large batch of pipes disappeared under the walkway, about halfway to the other end of the room, 20 meters from you. That was where the building plans indicated the exit into the sewers.
You saw steel stairs leading down to the floor, almost at the other end of the room. Another door led out at the other end of the walkway, closed. And you saw, heard no movement inside.