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Spend a summer afternoon at the lido in Thun: swim in the pools or the lake, then stretch out on the grass. Check the seasonal opening hours and admission before going. At other bathing spots, look up the facilities first; changing rooms, shade and lifeguards vary from place to place.
Pack a towel, dry clothes and sun protection. Use a public entrance, read the notices and look at the water before getting in. You need a comfortable way out, too. Keep children close and watch them throughout their swim. If the weather or water looks wrong, stay on shore.