Hello all, any suggestions for good hotels and (culinary) restaurants on the Belgian and Northern French coast? We happen to have three mid-week days in that area at the end of September. Thanks!

How far west in Northern France? We loved seeing Dieppe, Etretat, and Deauville in latter September some years back, but you may not wish to be that far west in Normandy. As to Belgium, Bruges is a beautiful city, and it is close to Ostend which is on the coast. Lille is in NE France, but never made it there. DeHaan is an old beautiful seaside resort, but when we were there, in third week of September, it was pretty well buttoned up. We day-tripped only. You would have to check with their hotels. Bruges offers lots of choices, and does not require a car, the train can take you to Ghent or Brussels, but we liked Bruges far more than either of those. I would definitely stay there on one of your midweeks. We opted for a beautiful guesthouse on the canals, but there are typical hotels too.

Dieppe has a line of great mussel restaurants down the harbour front, all straight off the boats over the road.

No recommendations on where to stay or eat (we were in a campervan) but the Cote d'Opale which stretches from the Belgian border to the Somme estuary is for the most part beautiful, with the Caps Griz Nez and Blanc Nez. Great views of England on a clear day!
The Somme Bay/Estuary is a wonderful area too. There is an old railway steam line which connects some of the villages around the bay.

I had a good meal at AuxTrois Suisses in De Panne on the Belgian coast. (Nieuwpoortlaan 28)

If you are staying in Bruges, Knokke-Heist is just a small hop away. It is a fancy seaside resort with a casino (more adults than families), and you might like to try its restaurant, Mascotte. Nearby is the nature reserve Het Zwin, on the border.

Lavandula

Belgians take beer very seriously, trust them.

Great idea's and suggestions! Thank you all. I'm going to do my homework now, best homework ever!

Bruges has a tavern in existence since 1515, a few blocks from the square, where the locals flock: Tavern Herberg Vlissinghe - ancient interiors with long tables for classic meals. If beer is really your thing, find the hidden in alley De Garre, a tiny pub which serves a "triple" of 11% amongst their dozens of choices. My husband managed that one well, but I stuck with my wheat beers.

Knokke-Heist has some really excellent restaurants, if you are going there. Also just across the border in Cadzand-Bad.
We like cycling from Knokke to Cadzand or one of the other villages in Zeeland, have lunch and cycle back. If the weather is agreeable, not fun in the rain. You can rent electric bikes. Damme is very nice too, with good restaurants.

The Hotel La Reserve in Knokke has just reopened it's restaurant, run by top chef Peter Goossens, with a menu of Belgian and French Classics. In Cadzand the Strandhotel has restaurants run by Sergio Herman.

@Tulips and all others: thank you again for all your suggestions. Much appreciated! We have decided to concentrate on the Dutch and Belgian coast instead of going to Normandy. We were lucky enough to find a nice room at the Strandhotel in Cadzand. We'll treat ourselves to dinner at Pure C.
Depending on the weather in September we'll have a variety of things to choose from in the immediate vicinity. Looking forward to it!

And don't forget the tram line that runs along the coast from the Dutch border to the French border.

Sluis (NL) is where people from Bruges go when they want a day trip somewhere. Quite different to Bruges!

Lavandula

In Cadzand Village there's restaurant Dell'Arte, and on the edge of the Zwin nature reserve we like Zilt&Zout. Retranchement is a pretty little village; restaurant Grenzeloos is nice. All are an easy bike-ride away. September can be lovely weather-wise.

The De Garre tripel is superb - - worth a journey. If instead of a journey you prefer a pilgrimage, there's the abbey of Westvleteren. They only sell their cases of what is often rated the best beer in the world, the Westvleteren 12 to individuals who register their license plate in advance for pickup in a specific time slot, but across from the abbey is their In De Vrede cafe where you can get a pour, and they sell 4-packs of the Westvleteren beers, though you can never be sure if they will have the 12 available on the day you show up:

https://www.indevrede.be/home.php?lang=en

4-packs of the Westy 12 at In De Vrede

I find buying flights is the way to go in Belgium. 4 or so at 8% is enough for me

Rent bikes and cycle to Knokke - most part along the boardwalk - for lunch at Sel Gris. You won't be disappointed.

I always enjoy staying in Le Touquet. It is a delightful coastal town, Good promenade. A range of restaurants and small shops… even a casino. Favourite hotels are The Westminster and The Bristol.

@MiriamC and UKtravelover: Again, thanks so much for all your tips and suggestions. I am busy compiling a list of restaurants and places to see and I know already that a midweek break will be far too short!

Elisabeth, I just read that Sergio Herman is stepping away from his restaurants in Cadzand. Pure C will close September 23. His other restaurant in Cadzand, Air Republic, will stay open until March next year.