When you live at the bottom, the only thing you have is to look up. If you're lucky you can see the lights of the great towers and the stars. If you're like most people, you just look at concrete. But the stars and lights are still up there.
These well crafted Dwarventi stairs lead down into one of the three main passages of Undertown. The underfolk have cleverly made it look like a short surface streets. Some of the branching passages look like streets as well, but it is all just a facade, soon they become more mine or hall like. The streets are “lit” (dimly by any topsider’s opinion) by mage lights and a few ancient amber Dwarventi Lights.
For all the aquaducts coming into the city, there munt be a place for the water to leave. Thus, many years ago, the Blackwater Tunnels were commissioned to carry sewage away from the city buildings.
The secret for immortality has been discovered by an eccentric wizard/mad scientist. Its found you need to reapply once a month. As people stop dying, and the birth rate increases exponentially, people are forced into homelessness, because of the need for food reamins the same, and food is not being produced fast enough to feed the undying population. The PCs have to find the creator and kill him, and destroy production, to save the world from undying, unending torture from hungryness.