<<"From what I understand the train goes directly into Zermatt, while for
the Jungfrau region we would depend on smaller connecting trains, which
may or may not be operational.">>
Rockoyster has thoughtfully filled in what I forgot to say.
Indeed, the meter gauge cograil trains to the population centers of Lauterbrunnen, Wengen and Grindelwald run all year long. The train up to Wengen from Lauterbrunnen is inexpensive inter "city" public transport. The same rolling stock continues to Kleine Scheidegg for some trains, and from Wengen onward to Kleine Scheidegg is a more expensive excursion train. At Kleine Scheidegg you may change for the cograil meter gauge excursion line down to Grindelwald Grund ( in the valley) and Grindelwald itself, just above that station. Or you may change at Kleine Scheidegg for the expensive run up to Jungfraujoch.
Also, on the Lauterbrunnen Valley side of the Männlichen ridge, access from Lauterbrunnen to the village of Mürren is provide by two public transport routes. One is a cableway from Lauterbrunnen to Grütschalp, on the plateau above, from which a train ( more like a trolley) runs along the plateau to Mürren. The other route runs by bus on the valley floor to Stechelberg, where the starter of a series of cableways runs up to Mürren. At least one of those two routes runs all year; maintenance is scheduled to always have one running.
From Mürren the cableways to Schilthorn run most of the year.
Here are the previous years' dates of maintenance shutdowns, quoted from the section about "Route."
"The cable car from Mürren to Schilthorn does not operate from 23 to 26
April 2019 and from 11 November to 6 December 2019. Services on the
route Lauterbrunnen-Grütschalp-Mürren won't run from April 29 to May 3,
and from October 21 to November 8 2019."
It is running on April 22 and 23 next year.
Checking the timetable for any specific date will tell you if a service is ( or is not) running.
This useful link provides few necessary tips and tricks:
Once you are comfortable with the subtleties, this is the direct link:
That site is full of many layers of information about rail travel.
The SBB has a free smartphone app.
Rockoyster uses it for all his rail, bus, boat and cableway planning. I find it to be invaluable while on the road, but prefer to do my pre-trip planning with the timetable mentioned above. I like the larger screen on a desktop computer.
Scenic trains have been mentioned. The route from Luzern to Interlaken Ost is one (meter gauge) segment of the Golden Pass routes. It has some nice scenery. It continues to Montreux from Interlaken Ost on standard gauge tracks, with a change back to meter gauge at Zweisimmen. That latter section down to Montreux is usually considered the most scenic section. In the future, through transport on the same rolling stock will be managed by changing the trucks(UK) (bogies in the USA) at gauge change points. A scheme to insert meter gauge tracks inside the standard gauge tracks on that section was abandoned in favor of rolling stock with changeable bogies.
Serious rail fans find this book by Anthony Lambert invaluable. It is published periodically with various titles:
Switzerland - Rail, Road and Lake-
smile.amazon.com/Switz erland-Rail-Bradt-Travel-Guide/dp/1841621323/re f=sr_1_3?keywords=Anthony+lambe rt+rail&qid=1572769356 &sr=8-3
Switzerland by Rail -
smile.amazon.com/Switz erland-BRADT-GUIDES-Anthony-Lambert/dp/1564407012/ ref=sr_1_5?keywords=Anthony+lambe rt+rail&qid=1572769356 &sr=8-5
It describes each segment of the rail system, including history, track/gauge, and sights along the route.
This map is well designed for travel in Switzerland, although Google Maps may show more hotels and stores. I like this one because of the features available from the menu under points of Interest/Traffic:
At zoom level 32, as shown (last number in the URL), the rail lines pop up clearly.
If you turn on "Traffic" under Points of Interest, you can get an overlay of icons for every station stop in Switzerland. Mouse over the icon, and you get the exact name of the stop, including cableways, city trams and buses, for use in the timetable:
map.search.ch/?pos=637068,160472&z=64 &poi=bergbahn,halteste lle,zug