My first attempt at creating a montage like this, so bare with me ;)
HDR from 7 handheld xps using the 16 mm f/2.8 Fisheye, sitting on the back seat of a Fiat 500. These were all shot in Livorno, Tuscany.
Cutout all windows and added my picture of San Quirico d'Orcia, Tuscany in a layer underneath. I removed the rear-view mirror in order to be able to see the cypress trees better. Most difficult part to me were fixing the reflections and shadows of the side-view mirrors.
Lastly, fixed the fisheye distortion with a plugin called Fisheye-Hemi by Image Trends.
All in all, hope you like the concept better than the technical execution ;)