We decided to take the train to Thun and ride the boat back to Interlaken, based on the late time for the first boat departing out of Interlaken. With our Swiss Travel Passes, the boat and train were both free.

This boat stops hourly in many of the towns, which allows more flexibility than we found in our Lake Brienz boat day (that one is every 2 hours). We found Thun itself a bit too busy for our taste, and ended up spending a lot of time in Oberhofen to visit the castle and then swim in the lake (it was during the late June heatwave). The boat from Oberhofen to Interlaken was just under 2 hours.

Interestingly, I saw many comparisons which say that Lake Brienz is more picturesque than Lake Thun due to being more green in color. Honestly, they were pretty similar - we had bright clear days for each lake trip and the water was an amazing bright blue-green for both. I think the choice would come down to how much time you have (Lake Brienz smaller) and which lake towns catch your interest. Both were awesome.

We took the boat from Spiez to Interlaken West which was free with our Swiss travel pass.
They leave every couple of hours or so.
It made a fair few stops at quaint little places along the way & made both an enjoyable & relaxing 1hr 20 minutes .
I would definitely recommend travelling by train to Spiez & returning by boat to either Interlaken West or Thun, which takes a bit less time 😊

Love Thun and come back a few times whenever I’m in Switzerland (stay with family near Bern). It has it all - nice relaxed cafe culture, lovely shopping streets, the river splits in two and is a nice place to wander or sit. The old town has some very interesting buildings and interesting shops. Then there is the beautiful lake and the mountains. On top of this all the great sights of the Berner Oberland. If I was to live in Switzerland I would live here.