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Lake Thun is not one uniform place to stay. Thun gives you old-town streets and restaurants; Spiez combines the bay with railway connections; Faulensee and Einigen are smaller, with more depending on the exact bus stop and address. Choose the daily journey you want before choosing a balcony photograph.
For time on the water, check the boat sailing and a return by land. A shoreline walk can be enough of an outing, especially between Spiez and Faulensee. Lake views do not guarantee direct swimming access or a flat station walk. Compare real accommodation, parking and transport costs; a lake stay is not automatically cheaper.