Mimoyecques is OK, but a right mess. Eperlecques (or as Watten) is much more substantial and although the museum aspect with random vehicles is nutty, the overall experience is good. If you visit the Batterie Todt museum at Audinghem on the coast below Calais at Cap Griz Nez make sure to walk past the little café outside (great steaks and moules - plus a weird outside loo) and go down the road to see the other casemates.The road arches round to the left. Continue along and you will come to the wreck of one casemate on your right. There are three. One is a bat sanctuary in the woods to your left, but the gun port has a viewing platform. Amazing fungi in the woods around it as well. The one on the road was completely destroyed by a Tallboy bomb, worth looking at the destructive power. The third, reached down a path on your right, which is nearest to the coast; is amazing. It has original German graffiti and murals in the lower accommodation and magazines. This is quickly vanishing due to modern graffiti artists work - so don't delay. There is a picnic site as well. It's all free access in a country park of sorts.
MB