Hello Loavoophaick14
Do you mean the Landwasser Viaduct? It is not in Bernese Oberland, it is in the Grisons.
Yes, you could travel via Tirano - St. Moritz - Chur - Zürich with a Saver Day Pass, but it takes about 10 hours and you must be sure that the selected train runs over this viaduct. However, in my opinion, the most beautiful part of this journey is the Bernina line.