If you say North West then you're going inland away from the coast.
There are a number of places to go. One that I've been meaning to go to for a while is the Nasicaa sea zoo in Boulogne.
http://www.nausicaa.fr/Anglais/accueil.htm Boulogne is also nice to walk around especially the old walled town up the hill. You can walk round the wall as well.
A few years ago my wife and I went to the town of Arques.
http://en.wikipedia.org/wiki/Arques,_Pas-de-Calais Arc International is huge and has factories all around the world as well as its founding place. They own a surprising number of names including Pyrex. Arques owes its existence to the glass factory there and there are tours round parts of the works. It's all in French though.
Not too far away is the village of Cassel
http://en.wikipedia.org/wiki/Cassel,_France where the Grand Old Duke of York is supposed to have marched his men up and down. To be honest there's not much there but you can drive to the top. There's what appears to be an old school (very closed when we went) there but we stopped for a picnic and to take in the views of the very flat surounds.
A bit further inland is the Ardennes region. Both in France and Belgium it's surprisingly hilly and very pretty to drive around.
http://en.wikipedia.org/wiki/Ardennes
Apart from this all I can suggest is you get loads of leaflets from the Office du Tourisme in Calais and, above all, just drive around slowly on the back roads with your eyes open!