Hi Alpenrose -
I certainly envy you for your stay from August through October. Great time of year, too.
I think I would see too many mountains one after another on the four passes bus route, but I've been on most parts by car or by bus or train. I've enjoyed stopping at Grimsel Hospice for lunch and history.
My reference book is Lamberts's "Switzerland by Rail" published by Bradt. I can see I misnamed the author (Anhony Lambert) and used the publisher's name by mistake above. Oh well, "Bradt" is prominent on the cover.
It is a 1996 edition, also published here in the USA by a nearby publisher in Old Saybrook, Connecticut.
In any case, it is a lesson in the conversion of the Swiss Rail system to a high speed interurban network, because many of the interesting branch lines have been converted to bus routes. So, I have to check the time table.
In my case, the appeal is sometimes for the rail line itself, as opposed to the scenery.
But, the Treib-Seelisberg Bahn funicular on the Urnersee appeals for both scenery and equipment, as well as the destination and walks above the Urnersee.
For rail fans, exploring the varied gauges of the rolling stock throughout Switzerland is interesting. You probably have tried the well known Brienzer Rothorn Bahn, with its steam locomotives. The Schynige Platte Bahn as well...interesting because it is an 80 cm gauge rather than the more common meter gauge, for its many twists and turns, and as well as for the scenery at the destination. Last time I went by the Talstation, I did not see any of the old (electric) locomotives that look like bricks or large boxes. They were built in 1911, if I recall correctly, and were running not too many years ago.
Although the views of the Bodensee are nice, the appeal of the Rheineck -Walzenhausen line lies in its rolling stock. A couple of photos are attached. Not so great technically....they date from 2003. It has only one locomotive/car and is built to 1200mm gauge. Just a tad narrower than standard gauge.
In Welshland, the Train des Vignes is worthwhile, with a stop for lunch overloking the lake and vineyards. Especially beautiful on an afternoon in the harvest time.
www.switzerlandbyrail. com/trains/scenic/lava ux_wine_train_vevey_ch exbrex.htm
On the left of that page form that link are listed some other "special" trains.