Hi Adrienne -
Thanks for the time limit. There are certainly very nice things to see and do within 1 1/2 hours, and quite a few more as you stretch that limit a bit. I always consider the train rides and the views as a treat, not a burden, so you might find yourself willing to go to Bern (at about 2 hours) for instance. Geneva is a stretch, (2 hrs 15 minutes) but, once again, it is a nice train ride.
How many days will you be in Chateau d'Oex? What part of the month? The weather is quite different from the beginning of April to the end, especially at elevations such as Chateau-d'Oex is at.
Montreux ( on the Golden Pass route) comes to mind, as Annika noted. The train ride down into Montreux through the vineyards is a wonderful experience. Lots to do near Montreux, too, and it is only about 1 hour away.
You can pick up a lake boat at Montreux, too.
If you go the other way on the Golden Pass route, to Interlaken, you'll spend 2 hrs 6 minutes on the fast train. Interlaken is not much of a destination in itself. It is what is nearby that is extraordinary, but it will take significantly more time to reach those locations, and the higher trails (easy, scenic ones) will be snowed in. Some services will be shut down between seasons then, too.
Gruyeres is a nice visit, although you will surely find plenty of tourists there. 45 to 52 minutes from Chateau-d'Oex
Just slightyly over your 1 1/2 hour time limit is Fribourg, at 1 hr 49 minutes. I particularly enjoy the old town, down by the river. You reach it by funicular from the park that is a couple of blocks southeast from the train station. Or, you can take a bus, or walk down the long flight of stairs beside the funicular.
Lots of places to eat and watch the tourists and citizens walk by, if the weather is sunny.
My Switzerland.com ( the Swiss Tourism website) has lots of information about destinations and things to see. If you have a town in mind, see what they have to say:
Once you have identified a town, locate it on the map for perspective, and use the timetable for travel times and routes.
I suggest that you use a map and a timetable in that fashion to look at possibilities. The timetable changes on December 15th, but the times for current travel are good enough for estimates. (Boats and cable cars have a schedule that varies substantially from season to season, so those need to be checked for the particular date being considered. But, you can get a idea of timing for boat rides from current timetables.)
One map I like -
If you zoom in enough to get icons for train/bus stops, you'll get transport schedules in a pop-up window for that station)
The time table -
The timetable defaults to the fastest route. So, you may have to use an intermediate stop in the "connection" or "via" box to force the routing. For example - for Luzern to Montreux, and specifically, Interlaken to Montreux, you need to go via Zweisimmen, or else you'll get the faster but less scenic routes through Bern.