Best Switzerland city stopover for train route starting in Paris and ending in Florence?

I'd recommend Luzern/Lucerne. Its a gorgeous city set on a river and lake surrounded by mountains. The city itself is fairly flat. There is enough to do, or plenty of opportunities to relax. You could consider a boat ride and then a cog wheel train to the top of Mt. Rigi.

There are several train routes available to you. There is one thru Dijon, France, and another a bit longer that goes to Strasbourg and then thru Alsace which would be scenic. That's the one I'd pick.

From Luzern, It looks like about a 6 hour train ride thru Switzerland, the lake region and Emilia-Romagna region. Sounds like another nice ride.

You would have train transfers on both routes, BTW

I will assume is this will happen after September 8.

If you want a city, Luzern is your best bet IMHO. TGV-Lyria train to Basel and change there for a train to Luzern. Luzern to Florence is to Milan, then change to a train to Florence. Luzern to Milan will require one change along the way. By mid September, you will have the option of going the fast way through the newly operational Gotthard Base Tunnel (~50 km), or the sceinc way mostly over the Alps with a shorter tunnel. The fast way saves about 1 1/2 hours.

You can look at tickets at www.sbb.ch/en

You might check out the website The Man in Seat 61 who has multiple recommendations and info on some closures. One he recommends is Paris to Zurich the Zurich to Florence which includes one of the scenic rail lines.

You might also consider Lausanne as a stop over. Its a lovely city on Lake Geneva. Very scenic with a few interesting museums like the Olympic one and some day trips. Hotels will give you a free public transport card for the metro and buses.

I believe the best route for simplicity, ease of connections, and an excellent Swiss city for a stay of 2 nights, is the one recommended above, Paris to Luzern (5 hours, one easy change at Basel if you depart Paris at 10:22 am. From Luzern you head to Milano Centrale, with one change on the way, then take the fast direct train to Firenze Santa Maria Novella from there.

Luzern is a lakeside town with a pleasant oldtown area and hotels and restaurants right on the river, close to the lake. One possibility for your full day there would be an excursion by boat, cogwheel train and cablecar to Rigi, “Queen of the Mountains”, nearby.

https://www.rigi.ch/en

Or simply take a relaxing cruise on the lake.

It might be best to sleep in Zurich instead of Lucerne (Luzern) because there’s a direct train from the Paris Gare De Lyon train station to Zurich’s main train station (HB) taking 4h 15m. There are no direct trains from Paris to Luzern. After a night’s sleep take a direct train from Zurich to Luzern for the day (45m).
On the day you go to Florence take a train from Zurich HB to Florence that requires a transfer in Milan taking a total of 5h 45m. If you sleep in Luzern, you’ll have multiple connections instead of one.

The connection at Basel for Luzern (Lucerne) is really easy and the station itself rather scenic with a huge mural over the booking hall, and Luzern is perfectly situated and beautiful as mentioned above.

The lake boats are right next to the station, and the old city (Altstadt) is just a couple of minutes away.

Gentle walking is easy there, and for just chilling the boats do that perfectly. The route up and over Rigi mentioned by Lola is easy and exquisitely beautiful, and really fun for any age.

Everything in Luzern is convenient, and if staying in Luzern your hotel will give you passes for local buses and trains (only valid within the city).

There is a current thread talking about Rigi - https://community.ricksteves.com/travel-forum/switzerland/mt-rigi

Paris - Luzern is really easy, and the fact that there is a train transfer involved should not put you off. Changing trains is a normal and expected feature of train travel.

If this trip is in September or later getting from Luzern to Florence will probably only involve one transfer.

We found the Basel station to be very nice and easy to navigate. To me, it would be much more work to overnight, one night in Zurich, then get back to the station and head to Luzern for just one night. The scale of Luzern, the close proximity of the train station to the historic, mostly flat city center, make it ideal for your needs. And then, Luzern, is really special. So many times when mobility is an issue, a traveler might need to compromise. Luzern is not a compromise.

Thank you everyone for the thoughtful replies! Unfortunately we have to leave Paris on Sept 6, so perhaps still experiencing some of those closures.

I probably should have specified that city doesn't need to be urban, we're hoping for a scenic and nature/culture focused stopover, so if that changes anyone's suggestions too I'd love to hear an alternate option - someone I know mentioned Interlaken?

I'm looking at the seat61.com recommendation for Bernina route given I'll be heading to Florence after Switzerland - anyone have experience with this route?

https://www.seat61.com/trains-and-routes/bernina-express.htm#Bernina_Express_to_go_from_London,_Paris_or_Zurich_to_Italy

I think of Interlaken more of a transportation hub. Have you looked at photos of Luzern? There are both city and nature scapes. We did the Bernina Express from Chur. It was lovely, but honestly, every train ride I've done in Switzerland has been lovely.

You could take the train from Paris to Chur, but there is not as much to do in Chur, and Chur, while lovely, is not nearly as pretty as Luzern.

Great tips, thanks Jules!

If you take the suggested route via Luzern you will not be affected by track closures on your travel date. That issue is on two of the other routes between Switzerland and Milan.

The Bernina Express gets lots of love on this forum, and from the Man in Seat 61, but it works best for people who are heading to Varenna on Lake Como, and have more days to travel than you do. To reach it, you must travel far to the east, to Chur, then at the end of the train journey over the Bernina Pass, you travel back west from Tirano to Varenna. And right now there is a bus link in place between Tirano and Colico, where you meet the train to Varenna. That is scheduled to last through Sept. 8, land would mean yet another transfer, with luggage, between transport systems.

You can see the various routes on this map of the Swiss train system, with the scenic routes highlighted.

https://www.travelswitzerland.com/en/download/swiss-travel-system-map-en-2023/?wpdmdl=14294&masterkey=63a023c8da36c

I suggest you look at the very scenic Gotthard Panorama Express from Luzern to Lugano instead of the Bernina Express. This is a journey by lake boat down the length of the Vierwaldstättersee (aka Lake Luzern) to Flüelen, where you meet a train for the rest of the journey, over the pass, to Lugano.

https://www.gotthard-panorama-express.ch/en/

I find the route over the Gotthard Pass even more scenic than the Bernina route, and this option adds the very attractive boat trip. We did this last September with our son’s family, using the regional train instead of the named Panorama Express. Everyone loved both the boat ride and the train, with snowy peaks, hanging glaciers, and lots of waterfalls even in late September.

While we took the less pricy regional train for this, I am recommending the actual Gotthard Panorama Express to you in part because they offer checked luggage service for the transfer between boat and train. You check your bags at the dock in Luzern and pick them up in Lugano, where all you need is a taxi to your hotel for the night.

https://www.gotthard-panorama-express.ch/en/stories/luggage-service

So—-one night in Luzern, in a hotel with view of the river if you like, then the boat plus train right to Lugano, for your second night in Switzerland. The next day take the train the short ride from Lugano to Milano Centrale, where you take either a Trenitalia or an Italo train directly to Florence. Italo is a private company and they offer senior rates as well as other discounts. Their website is very user-friendly. Trenitalia has senior rates only if you join their Carta Freccia program, but they do have other discounts possible. Some have reported difficulty with Trenitalia, particularly with certain US credit cards. Also you must use the Italian names for all the stations, so look for Firenze S.M.N. For your Florence destination.

https://www.italotreno.com/en

https://www.trenitalia.com/en.html

Total number of transfers between trains with luggage: one at Basel SBB, and one at Milano Centrale. From Luzern to Lugano you can use the checked luggage service if you take the Gotthard Panorama Express; otherwise you will have one more transfer between Luzern and Milan.

Wow, Lola. Got me Sold!

Wow Lola! Thank you for this incredible insight, there's so much to research and nothing beats hearing your personal experience and breakdown of the journey. My parents will be so excited for our upcoming trip, they've always wanted to take the train and see these parts of Europe - so thank you again for the input :)