Vaddooi is a self-sustaining city made up of an inner and outer ring, much like a bicycle wheel. The city itself sits on the inner ring. Small ball bearings separate the inner ring from the outer ring. This allows the outer ring to roam the terrain, leaving the inner ring, the city, suspended in the air while benefiting from the resulting friction that is used to power the entire city. However, the city's movement is not entirely arbitrary. Since the city relies on momentum, citizens must ensure to pick routes that take advantage of downward slopes and steer clear of those that lead them into pockets they can never return from.