That's a cool bridge, luvs. I would add some world scale dirt to it (slightly Y-stretched ridgy or mixed fractal, with the dark color slightly upped (0.1) into the color input of default shader). Als decrease saturation of background grasses (add blue node 'saturation' with fractal as input, and get some more variation in it, lighter darker (add multiply color, with fractal as input), feed that into main grey color of surface layer or as child.
Also increase tree coverage and more variety. And maybe change clouds into more sunny. Worth it!
