This started life as a 3D model on SketchUp. I used a plugin called Flattery to collapse the polygonal faces to a single plane, and then printed the parts from a screenshot. I hand-detailed the parts with a sharpie, then folded them and pasted them together.
I think people who have followed my 2D artwork on this stream will noticed it isn't at all a departure from my flat artwork, in terms of visual style.
Very clearly inspired by Howl's Moving Castle.