Best use of time between Lucerne and Mougins
 

We have a cruise (with Lucerne extension) that ends August 24, 2023. We have a week in Mougins, France, that begins August 27, 2023. That leaves us with two full days and three nights to spend somewhere. I'd love to hear some suggestions. We've thought about the Dolomites, Lake Como, and Cinque Terra. Ideally, we would not rent a car.

Don't forget that a train ride from Lucerne to Cannes takes about 10 hrs, Genoa is about halfway.
As you are obviously not interested in cities or in the Alps, a stop over along the Italian Riviera (5Terre for hiking; Sestri, Rapallo, Alassio, San Remo, etc. for beach life) could make sense.
If you pefer North IItalian lakes, I would stop over at Lugano, directly along the Lucerne - Cannes itinerary (logistically much easier). All famous places around Lake Como and Lake Maggiore are of easy reach from there, by boat, bus or train, according to your preferred itineraries.

Hi jbwitaly
How about spending some time in the Swiss mountains? Interlaken is a good starting point for excursions to the amazing Jungfrau and the Lauterbrunnen Valley. But if you want to be closer to the mountains, the villages of Grindelwald or Wengen are more suitable. This area offers the most diverse excursion possibilities!
Have a great trip!
Martin

Definitely agree with Swss_Sights --- you can head to the top of the Alps using just trains and cable cars. You can take the train up and base in one of the villages in the Valley or further up (like in Murren). August is a fantastic time to do it and the mountain view from the Jungfrau ("Top or Europe") are fantastic. Then you can return to the Zurich airport and take a flight to NCE or take the long train ride. (I used to live in Switzerland and now have a place on the French Riviera). I've been to Lake Como many times and while beautiful and wonderful, I'd still prioritize going to the top of the Alps in August. You'll have a week in Mougin and so you'll have some time to explore the coast there as well. .