The Dark Cloud is a nasty mix of chemicals and pollution that separates the top third of Southwatch from the bottom two-thirds, although it can move depending upon the wind and can shift without warning. Some believe the Fae control the winds that keep the cloud in place. Others believe the wind currents just meet here naturally and trap the cloud in place. And others keep their opinions to themselves.
Above the Dark Cloud—sunside—the colored bessem airships of the Aerie create bright blocks of color that tint the buildings below and the top of the Dark Cloud. But below—darkside—is another story.
The darkside neighborhoods are primarily populated by the industrial workers and their families, along with the merchants and street peddlers, the underground criminal element and the dispossessed. Needless to say, this is not a place that the well-to-do frequent. The air darkside can get thick with toxic fumes which can choke a person or melt their skin within a matter of hours, and on bad days the sunlight cannot even penetrate the Dark Cloud, casting the lower sections of the city into perpetual gloom. People who venture out onto the darkside streets on those days must wear protective clothing, sheltering their skin with coats, cloaks, gloves, hoods, and boots, guarding their eyes with goggles, their lungs with respirator masks. Many wear this gear regardless, warding against sudden shifts of the Dark Cloud. All of this makes for a restless, dangerous pulse constantly hammering beneath the sidewalks of the city.
The area within the Dark Cloud is considered a dead zone. The citizens of Southwatch can take the immense public lift system to travel through it, but nothing can live permanently in it. Nothing natural that is.
The only people who can successfully navigate the Dark Cloud belong to the ancient order of the Angels of Steel. The Angels primarily serve as a high-end messenger service, keeping communications flowing from those who broker power on the sunside of Southwatch to those who serve the powerful darkside. The Angels are all women who have been trained to fly with large wings powered by aether engines. The Angels have a secret navigation system that allows them to safely negotiate the twisted, invisible maze of buildings, tubes, and long-deserted streets concealed within the Dark Cloud. But while the pirates and crime lords would love to capture an Angel of Steel, thereby gaining not only her precious pouch of messages but her wings and her navigation system too, the few who have tried met up with the Angels of Vengeance—a corps of male Angels who spend their time—ALL their time—protecting their sister Angels. Woe betide the pirate who falls afoul of the Angels of Vengeance. Most of them end up as wide-flung splatters of goo, dropped from the upper reaches of Southwatch to the ground thousands of feet below.