<<"you could start in the Upper Engadine as Slowpoke suggested.">>
That is certainly a good target.
I actually had in mind a route for the more adventurous, through the Lower Engadine, and one which is not on the normal tourist track.
It is not simple to do, so I'll only give details if there is interest.
In general - Salzbruck to Merano via Innsbruck and Bolzano (Bozen).
From Merano, the fairly new train route through the Vinschgau to Mals Venosta Bus from there into Switzerland at Müstair, through the National Park and the Val Mustair to Zernez.
From Zernez, you are back on the Swiss rail network, and could go to St. Moritz in the upper Engadine, or explore Scuol, and Guarda in the Lower Engadine.
Afterwards, take either the Vereina Tunnel or the Albula pass further into Switzerland, eventually to Zermatt.
I'd not recommend this for the first time visitors to Switzerland unless they wanted to get off the normal tourist track. It will take more time than the route through Feldkirch.
If you stop in Bolzano ( Bozen) I can highly recommend the Hotel Greif.
If you really are a rail fan, there are several special routes in Switzerland.
The best by far, in my opinion, is the Gotthard Pass.
and do a Google search on Gotthard Pass Rail Route.
I'm planning to ride it somehow thsi year, especially, since i don't know what service they will maintain after they open the new tunnel underneath next year.
The Berner Oberland (Jungfrau Region ) has wonderful cograil train rides amongst spectacular scenery with some easy , beautiful walks. Starting and ending at public transportation.
try this one_
www.myswissalps.com/hi king/maennlichen-klei nescheidegg