A sky-cage.

Sky-cages were cages used as elevators off of the side of Sanctaphrax. They moved up and down on chains, and small flight-rocks set into the cage allowed for greater stability and maneuverability. Unlike hanging-baskets, which were used primarily for transportation between Sanctaphrax and Undertown, sky-cages were far more commonly used by academics to study Middle Sky and Low Sky, although Linius Pallitax used a middle sky-cage as transportation to and from the Great West Tunnel.