Infinite Helix
Natovis, better known as the Layered City, has seen better days. The upper layers are still intact and still governed by the authorities, but they are nothing compared to what they used to be.
Noone knows what goes on past the 8th floor down from the top. It is estimated that there could be thousands of floors. Things are so far declined that much of history and science is forgotten.
People turn instead to speculation, legend, and outright guessing to explain the world and universe. Most do not even know how the city got there.
There is a series of mysterious and unexplained disappearances, none of which have any evidence, except for one. The insolvency to fixing this problem shines light onto the civilizations decline. The public, lead by some extraordinary individuals take action to both solve the mystery, and turn things around.