Places to visit nr. St-Omer:
St-Omer Cathedral - one of north France's finest medieval buildings
Glassworks - Arques' famous crystal glassware factory, with shop
Boat trips - on river Aa and Audomarois marshes
St. Bertin's Abbey - ruined in the French Revolution
Museums: Hotel Sandelin & Henri Dupuis - St-Omer
Saint Omer Brewery - book for tours
Nearby:
La Coupole - grimly fascinating Nazi Second World War rocket base
Le Blockhaus d'Eperlecques - original bunker for manufacture of V2 rockets
Les Fontinettes canal-barge Lift - Arques
Distillerie Persyn - Gin Distillery (can visit by boat)
Dennlys Parc - family theme park
...near Aire-sur-Lys:
Thérouanne - archaeological remains of medieval cathedral
Loisinord ski resort, near Bethune - new use for an old coal-mine slag-heap
Azincourt Medieval History Centre - new exhibition by the battlefield
Fressin Castle - ruins of medieval castle near Fruges