Grindelwald to... where?

If you want more mountains, Zermatt? Gives you the potential to do
the Glacier Express train instead.

If you want lakeside scenery, Montreux? Advantage here is that it's easy to
get to Geneva and then back to Paris for (I assume) your return flight.

I agree that the Dolomites are too far away to be practical - probably the better
part of a day to get there, so 2 of your 10 days get eaten up with travel.

The Dolomites are indeed to far, but there are some great options close at hand.

I suggest you take the train to Luzern, spend time there or nearby, and then take the Treno Gottardo over the Alps to Locarno ( a journey that we find just as scenic as the Bernina Express, but much more convenient to reach). Locarno is a lovely Swiss town on Lago Maggiore, part of which is in Italy and part in Switzerland. After some time in Locarno, you can take a ferry on the lake to one of the Italian towns on the lake. Then fly our from Milan if you do not already have flights booked..

Here are some details:

Grindelwald to Luzern is itself a scenic train journey. You could stay in Luzern, which many people like a lot (but not us), or take a boat from Luzern to nearby Weggis, a small town on the lake 40 minutes away. We did this last September, staying at this lakefront hotel which I highly recommend:

https://www.gotthard-weggis.ch/en/

They have kayaks for guest use, and access to th3e outdoor pool at the sister hotel next door. And a lovely lakeside restaurant to enjoy.

Whether you stay in Luzern or Weggis, you can visit the nearby mountain Rigi. From Weggis iit is a simple cablecar ride up to Rigi Kaltbad, with beautiful views over the lake, and a spa hotel that accepts day visitors for the beautiful outdoor pool and other amenities. Or just go for a hike and enjoy the views over the lake.

https://www.rigi.ch/en

https://www.rigi.ch/en/experience/wellness

https://en.hotelrigikaltbad.ch/wellness-spa

From Luzern, you can take the scenic Treno Gottardo over the Alps to Locarno. If you stay in Weggis, you can can travel by boat across the lake to meet the train at Fluelen, making a lovely experience. We did this last September with our family. Or you can board the train in Luzern and ride to Locarno with no changes. Use the links on this page to see photos and earn more about the Treno Gottardo:

https://www.travelswitzerland.com/en/experiences/scenic-routes/treno-gottardo/

Locarno is a Swiss city in the Italian-speaking Ticino canton of Switzerland. There are nice hotels right on the lake just 2 blocks or so from the train station. We like this one, but there are others as well:

https://www.hotelgeranio.ch/en/

With several nights in Locarno, you can visit the nearby Valle Versasca:

https://www.ascona-locarno.com/en/explore/valle-verzasca

Note that the water in that river may be lower in September than what you see in the photos. You can also rent kayaks, or travel by ferry to island or other towns. Lots to do there. Milan is about 2 hours away by train if you want to fly out from there.

Congratulations! The train ride from Grindelwald to Lucerne is spectacular. You do have what many consider to be the most scenic train route in Switzerland in your plan— the Bernina Express route.
The best leg of this route ( which can also be seen from regular trains traveling on the same train tracks as the “ Bernina Express”) is between St. Moritz and Tirano, Italy.
If you stop about 8 miles beyond St.Moritz at the “Morteratsch ” train stop, you can walk a 30-minute flat and easy path to the tongue of the Morteratsch Glacier.
Another stop at “ Alp Grum” brings you to a trailhead leading to a turquoise lake far below. The lake is colored by the minerals in the glacial runoff that flows into the lake.
After the Bernina Express route, I would head for Lake Como for a few nights. Then to Milan to take a high-speed train to Lyon— France’s #2 city that is renowned for its restaurants— then on to Paris. From Tirano, it’s a 80-minute train ride to the train station on Lake Como called “Varenna-Esino.” There are frequent ferries here in Varenna that boat to Menaggio in 20 minutes and to Bellagio in 10-20 minutes.
From the Varenna-Esino train station it’s an 80-minute train ride to reach the Milano-Centrale train station.
From Milan, there are high-speed trains traveling to Lyon, France. And from Lyon, Paris is just another 2.5 hours away by high-speed train.
You can check train fares and schedules at www.TheTrainline.com
If the train fares are too steep, look into flights from Milan to Paris at www.Skyscanner.com
Have a great honeymoon!

From Milan, there are high-speed trains traveling to Lyon, France. And from Lyon, Paris is just another 2.5 hours away by high-speed train.

The Milan - Lyon line is still suspended, it will not resume until Q1 2025. There is a replacement bus in the middle section, but it adds a lot of travel time. I would do Milan - Lausanne/Montreux - Paris instead.

anastasia, Just noting that you saiid Turin in your post, when you likely meant Tirano. It makes a huge difference in checking railroad schedules.