No dark arts, just a few dark dreams due to lack of sleep.
Nothing is being rendered separately for comping as yet, just a straight render from standard deep edition, with a little exposure control in photoshop.
Lots of soft shadow lighting and a local volume receiving shadows, to help achieve the diffuse lighting.
The models are all imported at the moment, but that will change once the composition settles, and I'll be converting to vector displacement for more control and populating elements.
I agree about the bridge, it jars from that angle though it it looked correct in plan view, so needs addressing.