An interesting one JW. I should have looked at it on the laptop a bit earlier, I mistook the image and it would have saved a lot of time looking for a non-existant monolith. I had also looked at the structure a while ago when you set the river image, and the penny was very slow to drop.
And now for something completely different...
Where is this railway bridge? The finite number of railways and suitable topography for such a bridge means no clues yet, except that it is a live railway.