Calais

You probably wouldn't pick Calais as your beach destination of choice, but it does have some really nice wide sandy beaches and East towards Dunkerque out by the old Hoverport some dunes and wild areas, albeit back-dropped by a large cement works (I think its closed now though). Its a sort of strange, post apocalyptic place for a picnic.
The town itself was flattened in 1943/4 so there's not too much of interest apart from the City Hall which looks like someone went mad with an Edwardian version of giant-Lego - it has a certain charm of its own and from a distance can make you think "I thought we were going to Venice next week" such is its resemblance to St Mark's
Along the coast the other way is Bleriot plage - named after the French aviator who, 100 years ago in 1909, was the first the fly the channel. Just look out if you are driving along the D941 - there is a large fishing boat that looks as though it was tossed ashore and landed on the (surprisingly coincidental) roundabout b y accident one dark & stormy night. Thisn is a very French "thing" and perhaps the subject of another guide...