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Snow changes this valley completely, but a summer walking plan needs rewriting before you use it in winter. Decide whether you want a prepared winter footpath or a marked snowshoe route: they need different footwear and equipment. Ask locally which route is open and suited to the least experienced person coming with you.
Wengen is reached by railway from Lauterbrunnen, so include that connection and the walk to the route start. Allow for a slower pace, short daylight and the return train. Snowshoes do not make unmarked slopes safe. For unfamiliar terrain or uncertain conditions, choose professional guidance instead of improvising a route.