This is a mobile city from Philip Reeve's novel, "Predator's Gold", part of the "Hungry City Chronicles" quadrilogy. In the book and the model, the city travels on skis and its one drive wheel, or treads for better traction.
The model contains one minimotor, and runs on an outboard battery box tethered by a wire.
The horizontal cylinders on top are zeppelins, and the building at the back is the Ice Palace, home of the mayoress.
I actually built this, but I'm no photographer. All renderings done in LeoCAD.
Rear view. The tan rings around the the wheel are (approximated) rubber bands for traction.
Underside. Notice the two tiny wheels to avoid scraping when the wheel is in use.
The mechanism takes up the entire interior. The motor shaft is connected to the yellow pulley on the right, and the drive shaft slides back and forth with a worm gear to engage or disengage the drive wheel. The white gears are connected to a set of arms that raise and lower the treads. I had to use clutches there because the arms only move through about 90 degrees.
Here's a bird's eye view of the top tier of the city. The palace is on the left, directly in front of the wheel, and the zeppelin dock is to the right and down a bit. The gaps between buildings create some main roads, so it doesn't look like just a jumble of bricks (which it is).