We plan to set up base in Bern then in Zermatt and then in Lauterbrunnen. What would be best route to get to Oeschinen Lake. Could we do it as a day trip from one of these locations? Any scenic trains to take vs another train. Thanks!
By road, Oeschinensee is quicker from Lauterbrunnen (traveling first almost to Spiez, then turning south) or Bern--between 1 and 1-1/2 hours. The nearest mentionable town to the lake seems to be Kandersteg, and you can travel by train from Lauterbrunnen to Kandersteg via Spiez.
This schematic indicates that there may be a way to get to the lake from Kandersteg. It probably requires a bus (maybe Postbus) from Kandersteg, then it appears there's some sort of mountain railway for the last little bit.
Schedule info for the rail part of the trip is on the SBB (Swiss rail) website.
Info about travel beyond Kandersteg is here. Here it sounds as if there's also a mountain lift all the way from Kandersteg.
We day tripped from Wengen to Lake Oeschinen in early September. From Lauterbrunnen, train to Spiez, then connected to Kandersteg. From Kandersteg’s train station, it was about a 15 min walk through town to the lift to the lake area. After about 10mins on the lift, you have various trail options to get down to the lake. A lot of hiking options are available there. When we went, it was rainy so we didn’t get the views we hoped for, but I enjoyed seeing areas in the BO outside the Lauterbrunnen Valley. Also, we had the Berner Oberland Pass, which covers all travel (including the lift) fully.
Just take the train to Kandersteg and walk to the gondola that goes up to the lake. You can walk on the paved path to the lake. Thre is also a trail that goes around part of the lake to a waterfall (a little scrambling with a rope along a steep rock path) and through a small forest with interesting sculptures. There are several small inns with places to eat overlooking the lake. If you are feeling adventuresome there is an alpine slide near the top of the gondola...beautiful ride and views that are spectacular!