Day trips from Paris

Lyon yes but Colmar no because it is too far and touristy in the day.
I would go to Colmar or another town in the area spend a night or two and then to Lyon on your way back to Paris

We took a day trip to Lyon when we were in Paris in June of 2018. We took an early train there (took about two hours I think) and spent the day in Vieux Lyon with a friend who had moved there. Then took the train back to Paris that evening. It was really nice. We enjoyed the time relaxing on the train because we had been so busy in Paris we kind of needed a rest, and it was fun to see a little bit of Lyon.

Lyon is feasible as a day trip, but the trip takes over 3 hours each way once you take into account transportation at each end. Have a look at Dijon maybe, it's nearer and more manageable.

hey hey Jaime
do you know the way to San Jose??
had to, lived in Campbell. LOL
we are taking our third trip last week of September. we are planning to take the train to andresy, near Paris to have lunch on the river. ring the bell and restaurant boat comes to take you across to sit and relax, Auberge de la goelette. Thanks to janettravels here on the forum.
frenchie-FTG.com American hot dogs made fresh there
canauxmana.com take cruise down marne river away from Paris
we are thinking of going to La Rochelle, northern France, stay city center on the water. will keep our apt since we have it 8 nights, no sense packing/unpacking and moving. take overnight bag.
we also took the train to Reims and did a tour in those little french cars (cv2) thru town and out to vineyards, small villages, back to town we found cafe and us girls ordered different french champagnes of that region, not what we can get in states, did our own tasting. So much fun
look at how far and how many hours on train, plus schedules and times for your day trips, along with how long you have to enjoy town or village without stress and watching clocks/watches
eatwith.com mammazsocialfood.com getyourguide.com look up having dinner served at a parisian’s own home with others.
just a couple other options, have fun
aloha

So far my favorite has been to Chartres.

There are literally dozens of great day trips within an hour of Paris; I would not go a long distance.

Chateaux: Vaux le Vicomte, Fontainebleau, Malmaison are the three I would choose from if you want a chateau. There are others Chantilly, Maintenon, Sceaux, Rambouillet, Ecouen etc.

Medieval towns: Senlis, Provins, Crecy la Chapelle, Moret sur Loing. (dont' day trip to a small town on Mondays which is the day they tend to shut down)

Small interesting cities: Rouen for architecture quite different from Paris and Reims for the Cathedral and Champagne houses.

Chartres for the Cathedral and Auvers sur Oise where Van Gogh lived his last days
The gardens at Giverny and Monet's home.

And there are tons of things within Paris you have probably not done either -- there is another thread on secondary and tertiary sites running on this site.

Chateau Malmaison is a nice day’s outing and you can reach it by metro and then a short bus journey. Check out the website. There used to be and maybe still is, a nice restaurant right where you get off the bus. We had an excellent lunch there.

If you haven't been to Epernay it's a great day trip. Colmar is too far as is Lyon IMO.