Planning a river cruise on the Douro but thinking of arriving in Paris and touring Normandy eventually ending up in Porto. Has anyone had experience with the train systems.
The only practical way to get to Porto from France is a flight. From Paris, in your case. The rail connection to Porto is very poor, it would take 2.5 days!
Since Porto is a vacation destination even for the French, and if you don't want to go through Paris, there are a few direct flight options from cities like Nantes and Brest, to name just the ones that aren't too far from Normandy.
The train is not a viable option, you would have to travel across three successive national rail networks: French, Spanish, and Portuguese.