Takes too long to get into to Paris for a day trip to get to things without running around like a chicken with your head cut off, but Le Havre has some interesting things to see and you easily can hop on the train from there to nearby historic towns. You can also easliy rent a car in Le Havre, so there are definitely options for the do it yourself traveler.
We have been to Vigo before and just enjoyed walking through the park above the city and seeing some of the Celtic ruins there. Lots of little cafes and places to get some good tapas and seafood dinners. You also can hop on the train to get to Santiago de Compostela rather than taking an expensive ship tour there. Lot of shopping in Vigo too.