Want a mild apocalypse?
Right now I am playing a game set some time in the future in the city of new orleans. It's not exactly what you are looking for, but the same type of setting could be modified to include more fantastic elements.
Background
Welcome to the distopian future of "New" New Orleans. Between global warming and 5 massive super-hurricanes that hit the area between 2005 and 2015, the city of New Orleans was in pretty bad shape. The city, already below sea level, experienced nearly daily floods of toxic water from Lake Pontchartrain and the Mississippi River. The levee's were routinely topped or breached and the pumps could not remove the water fast enough. Add to that the desperate poverty and the city nearly descended into madness as criminal elements took over. New Orleans once again regains the title of "murder capitol of the world"; with per capita homicide rates equal to Mogadishu and Rio de Janeiro combined. In some neighborhoods, you had a higher statistical chance of surviving a self-inflicted gunshot wound to the head than walking 2 blocks after dark. The citizens had enough and took to the streets in protest. Hundreds of "rioters and looters" were slain and thousands beaten and arrested by local police before the people returned to their flooded homes, but at least someone listened.
A massive public works project began to elevate the city above potential floodwaters and provide much needed security for the every day people of the city. Massive water and wind proof towers were built around and within the city. Each one of these towers is virtually a city unto itself, with apartments, industrial and commercial areas to support a community of over a hundred thousand within each tower. While by no means beautiful, these towers are efficient and relatively safe, though some criminal activity has yet to be stamped out. Combined these towers house the millions of everyday citizens whose hard work fuels the booming economy of the new city. On top of these towers, a massive platform with a surface area of nearly 400 square kilometers was built with a shiny new city on top. The new city is beautiful, clean and safe. Filled with elegant gardens, parks and fantastic restaurants, it is the hub of high culture and the residence of the cities wealthy and powerful.
However, all is not well in the new city. For one, the old city still lies within is shadow, now flooded with the murky brown water and much of it is denied direct sunlight during the day. People still live there, some because they could not find a home in the overflowing towers, some hanging on to their now valueless property, some to ply their criminal trade, and some because they are too mutated to fit within "polite" society. It is a place where people go to loose themselves, and on rare occasion to find themselves. It is a dangerous place, filled with disease and controlled by warlords, druglords and mysterious cults. But even they sometimes find themselves preyed upon by creatures lurking in the shadows and in the murky stagnant water. Most people here live on the upper stories of old buildings and use small boats to navigate the flooded streets.
The leaders of the new city are corrupt, nearly everyone says so. They "allegedly" live opulent lives, skimming and embezzling from the City Construction Project and accepting kickbacks from business and criminals while ignoring the plight of those left behind.
Occultism has been on the rise as well. Voodoo is a mainstream religion in the city, and a large number of newer cults have sprung up as well. Despite Voodoo's popularity, few believe the rituals have any power, and usually they do not. However, magic does exist, even though the general populous generally agrees that it does not. Those in the underground/old city are typically more accepting due in large part to their constant exposure to the unusual.
The toxic waters that entered the city decades ago are known to cause mutations among the children of those that have been exposed. Many people in the upper city often view mutants with distrust and disgust. They are commonly targets of persecution by the police and by "good ol' boys", often finding their only refuge in the lower city where there are entire communities of outcasts filled with people of every type, shade, and number of appendages.
Psionics are a fairly new development, only manifesting within the last decade. Few accept psionics as a fact; most view those claiming such powers as insane. Why psionics have appeared and how it works is still largely a mystery even to its users, though some organizations are known to be actively researching the topic.
I wonder if it has a ghost tower? 
