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 PCs encounter an elaborate trap room, designed to fill with water, drowning those inside. Clever and resourceful, they disable the trap and move on.
Only later do they discover that this room is part of the elaborate cooling system that prevents beasts of elemental fire from overrunning the complex. While the fiery beasts run rampant, they begin setting fires, which causes the complex to become increasingly hot and smoke-filled. Additionally, the PCs now have to fight their way out past aggressive fire creatures...