5-6 days in Switzerland in late September

In CH? If so, Bern would be my next choice that requires three connections from Gimmelwald taking a total of 2h. The first connection is on a cable car called the Schilthorn that will drop you off in Stechelberg (15m). From there you'll need to hop on a 15m bus ride to Lauterbrunnen before jumping on a train to Interlaken (30m) and switch train lines to get to Bern (1h).

I think Luzern would also be a good choice. Easy train connection and there are several interesting things to do. Boat ride on the lake is very nice.

sort of depends on your interests and perhaps where you are arriving in Switzerland (though you can get pretty much anywhere in a few hours). If you want to max out on mountain views and/or hiking, Zermatt and the Matterhorn are great and not exactly the same as the Berner Oberland. If you like charming historical cities, Lucerne is wonderful. Basel has lots of museums. If you love castles, Chillon (staying in/near Montreux) might be a good choice. You can't lose!

You could visit the Lake Geneva area via Bern. We day tripped to the latter (wish we would have also stayed the night) before spending a couple of nights in beautiful Montreux (wish we would have also had time for Vevey and Lausanne). Going the other direction, Luzern is definitely worth a few days (we only did one). Hope this helps!

We love Montreux and are starting our September trip there again. Then off to Lauterbrunnen valley. You could consider this, or as people have said Lucerne. Or Zermatt. Might depend on where you are going in Italy and how you plan to get there.

Thanks all!