Regionalpass Berner Oberland is the best deal ! by globetrott
Transportations around Interlaken are quite expensive, but at least you may save some money, when you buy one of the special ticket, available in a big variety : In case that you are lucky with perfect weather and stay in the area around Brienzersee & Thunersee for at least 3 days , it really makes sense to buy the "Regionalpass Berner Oberland" :This train-pass is valid 7 (220,-sfr) or 15 days (265,-sfr) and during 3 of these 7 or 5 of these 15 days you may use that ticket for unlimited travels, only for a tour to Jungfraujoch you pay 50 sfr extra and for Schilthorn 30 sfr extra - the Brienz Rothorn is totally included !!
The tickets are for 7/15 consecutive days, BUT you may choose any 3 (or 5) days of unlimited travels by yourself - you simply stamp your ticket at any trainstation into a machine on these days.
During the rest of the days you pay half of the ordinary prices.
This ticket includes also all trains and ships around Brienzersee and Thunersee, trains till Brig, Lenk i.S., Adelboden, Meiringen, Gstaad and halfprice all days to Zermatt, Luzern, Bern etc...
I had such a ticket with 7 days and could save a lot of money, although I had only 3 days with excellent weather-conditions !!.
See more details about that ticket on my link below !!