Hi there! My fiance and I will be travelling around between Amsterdam and Paris for two weeks in August. We have Ams and Brugge booked, but are wondering what to do for the three days before we end our trip in Paris. We had thought about renting a car but would rather take trains. We were thinking Rouen for at least a night. Any other suggestions for an artist and her WWII buff fiance? Thanks so much!
Your reference to "her WW2 buff fiancé"--this hints that your fiancé might be interested in the D-Day Invasion sights in Normandy. Unfortunately the beach battle sights are not accessible by train. To placate/or make your fiancé happy, you could sleep in Bayeux the night before and then meet the Overlord Tour folks for a great tour; obviously this would require advance booking with Overlord Tours or other tour provider.
I'd say Normandy is essential at some point for a WWII buff. Three days (maybe only two nights) is enough to get the gist of the main sights. I recommend renting a car, though. Driving in Normandy itself is easy, and you could go and see all the sites yourself - or, take a tour one day and spend the second day re-visiting sites you want to spend more time at or others that were missed.
It might wind up being easier to take the train to Paris and either take the train back up to Caen and rent a car there or rent the car in Paris itself and drive up. I did the former when I did the tour a few years back - in fact, I did almost exactly what you are doing but in reverse (Paris - Normandy - Belgium - Amsterdam).
Normandy the logical suggestion.
Maybe this: Train to Lille, drive to lovely Honfleur for the night. The next day, drive to Bayeux & spend 2 nights, as a base to visit D-Day sites or take a tour. Return car and ride the train to Paris.
If that is too fast paced, consider just adding the time to Paris and planning some day trips: to Rouen, to Fontainebleau, or any number of other great places.
Normandy is one option, but you'll need to backtrack to Paris. If you want to do Rouen you can easily do it as a daytrip from Paris.
If you'd rather choose something between Brugge and Paris I recommend a stop in Lille.
It's an easy trip by train from Brugge(less than 2 hours with one change) and than on to Paris(1 hour by frequent TGV(=high-speed train).
While you're visiting the rich, but uncrowded collections of the Fine Arts Museum of Lille and the Louvre North in Lens, your fiance could rent a car for a day and explore some exciting WWII sights(although this area is more famous for WWI) like the Todt Battery and its mighty rail gun near Calais or the massive bunkers of Eperlecques and La Coupole.
You haven't mentioned the rich and popular ( and easily train-traveled) other cities in Flanders: Antwerp, Gent, Brussels, Leuven, Lier, Mechelen, and more.
Your previous bookings suggest it’s too late to consider adding Leiden, den Haag, Delft, Rotterdam, and Kinderdijk.
Lille is certainly worth to consider, especially the old part, Vieux-Lille has a nice intimate atmosphere with it’s many cobbled streets, shops, cafés and restaurants and invites to explore. There are besides the already mentioned fine art museums several contemporary art museums and galleries like Lille Métropole Museum / LaM and La Piscine in adjacent Roubaix. Here an overview of the museums (French, English not available now). https://www.lille.fr/Que-faire-a-Lille/Envie-de-culture/Musees-et-expositions2
Not that you mentioned this but how about visiting the champagne region as it lies between Brugge and Paris. Stay in Reims and visit the lovely museums AND drink some amazing champagne while you're there.