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You don't state which part of winter you are going.
If it is 'peak' winter e.g. Feb here is my album from a Filisur stay in February 2012:
http://gwizz.zenfolio.com/rhbfeb2012
I did not attempt the viaduct path partly because the Landwasser view is very rocky so winter shots are not so different from summer shots.
BEWARE: Another very good reason for not attempting the Landwasser paths is that they may be officially closed at the time of your visit. You can forfeit your chance of insurance or indeed rescue if you traverse a Swiss footpath that is not an official winter walking path. Official winter walking paths (with pink signs) are different from the normal yellow signed paths.
In my opinion it is better to venture to spot where acres of snow such as Bergun and Preda
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