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Walk from First to Bachalpsee, eat your picnic beside the water and return the same way. On a still day, the peaks reflect in the lake. Allow about two hours for the walk itself, with extra time for the gondola from Grindelwald and a stop by the shore. There are uphill stretches, so bring walking shoes and water.
Look up the trail status as well as the last gondola. Snow can keep the path closed while the lift is running. If you are tempted to continue towards Faulhorn, look at that route separately before you leave: it adds a much bigger mountain walk.