We saw the French film "Seraphine" [highly recommend the film, by the way] & are intrigued by the town of Senlis. Has anyone visited? Is it worth a day trip?
Great little town, but I tend to track down anything that has to do with the Celts. You could easily spend the whole day there. It beats the Loire chateaux, but not Chartres. I've only gotten there by car, so will leave the feasibility to somebody else.
Be aware that if you're traveling by train anywhere in that area, you are subject to delays or being transported by bus as there is an ongoing "labor dispute" with the TER rail system. I've been to Amiens, Laon and Rouen recently - all very interesting towns, and I'm sure Senlis is similar. Laon has a very intriguing old district worth a visit and Amiens has a lot going on.