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Come for the view across Lake Brienz, then give yourself time to walk along the public shore and look back towards the village. A meal or a seat beside the water can be part of the visit. You do not need to make everything depend on one photograph at the pier.
From a Lake Thun apartment, include the journey to this other lake. Check the bus or boat home before setting off. Continuing towards Giessbach is a separate walk or sailing, not an automatic extra. Keep to public paths and respect the waterfront homes. The official village information helps you choose what to do.