Outdoors - Depth of field was real issue here. Note the sky reflections in the side of the freight cars. The sun was going down behind the camera and the diorama was in shadow. But the trees beyond it were still lit. This lets those reflections (and the ones on the spur track rails) really show.

This picture would have been nearly impossible indoors because the reflections would be of benchwork, the ceiling, and other stuff instead of the sky.

I love that crummy looking trackwork on the spur!