Either way, it is worth the trip. Interlaken RULES. Stay at Baumers H. ... you'll be able to find it.
Driving from Dunkirk to Calais, France 29.8879543 miles 48.1 km - about 35 mins
Other sites tell me it is 72 miles!
580.97 miles (934.98 kilometres)
58 kilometres taking E40 (EST). Andinkerke is the first exit in Belgium.