This shot of Dorothy and Roger approaching the factory isn't simply an exercise in great composition, it's actually effective foreshadowing for both the true nature of 'Dorothy' and the final confrontation at the end of the episode. This huge doorway tells the audience that something on a mighty scale must have been constructed at this location and no exposition needs to be given.
Visual storytelling, who'd have guessed that such a thing would catch on?
I haven't seen the first episode in some time, but are those supposed to be rails running along the ground there?