We first took a train from Interlaken to Spez, and then took a boat from Spez to Thun. Lake Thunersee is known as God's left eye. I personally think it is a little worse than Lake Brienz, God's right eye. Lake Thun is greener, while Brienz is bluer. Of course, Lake Thun is also very beautiful, especially with the buildings and natural scenery on both sides.
If you take a boat, it is free with a Swiss pass. However, there are few seats in the second-class cabin, and it is a bit cold to sit outside. It is recommended to wear more clothes.
From Thun back to Interlaken, we chose to take the bus, and we can see different beautiful scenery along the way.