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Segelschule Thunersee offers introductory sailing courses around Spiez and Hilterfingen. You get to try handling the sail, with the lake and mountains around you. A yacht outing with a skipper is another possibility; ask the school about it directly.
Arrange the date and meeting point with the school, including what happens in poor weather. Winter theory classes take place ashore, so choose an on-water course if sailing is what you have in mind.