A lot of things going on here; so, I'll leave the interpretation up to you. Roughly, I built the two cityscapes in Blender. In Photoshop, I added steam from the buildings' roof-top units and fog, along with some other hand work to fix things that were bugging me. Then applied a number of filters to degrade the scene to a point where I was happy with it.
I'm really liking the texture (you have to zoom in to see that very well) on the buildings. Reminds me of ink sketching and watercolor.
The final image is 24in x 38.66in @ 150ppi. You can see the zoomable version here:
Process in a little more detail:
I started by constructing the cityscape in blender, using a particle system. If you ever have a need, Andrew Price posted a brilliant video tutorial that makes it pretty easy:
Once I had a basic city, I duplicated it and turned it over. I'm sure this is an easy thing for many people out there, but it took me a while (and a bit of trial and error) to figure out how to turn a particle system upside down. I'm still not completely sure I understand what I did. Let's call it dumb luck.