On my current map there is a waterway in the middle of the city, and there is a large sewer pipe that you can enter. It is not a normal POI and does not have a name associated with it (not that shows up, anyway), but I will give some details that you may recognize. It leads to a water filled room with a large cylinder in the center. You have to drop down into the water, and there are some zombies lounging on the bottom. There is a ladder in the center of the cylinder, but it is way to high to use. There is also a walkway with one section of ladder on each side. They look like they would be useable, but apparently they are just a tad out of reach. I could not place blocks beyond the first one since I could not jump, so I had to build a ladder myself and attach it to the existing ladder to extend it down to a place where I could use it to get out. The outside of that building is grey brick with two silos. The larger one has an octagon shape, and the smaller one next to it is round. I hope that is enough to go by. I can't imagine that this drowning chamber was intended.
