A good interesting fast route out of Boulogne, a good extension to the D940 coast road from Calais to Boulogne. There are some flat out staights, blind summits, off camber bends and a few tractors to keep you on your toes. Therouanne and beyond is nothing special but if you are going further, or back to Calais, there is a junction on the A26 a few km the other side of Therouanne making it a good round trip for a day in France.
BBR-David