The Landwasser viaduct is a very impressive piece of architecture and even more iconic when the red train is passing by. this happens every 20minutes roughly but check the schedule on sbb.ch first ro avoid too much waiting time. You have several viewpoints of this bridge and here I share the two best ones. Option one is the one underneath the bridge. The coordinates are 46.680293, 9.675336. From the parking spot its a roughly 20min walk and only 800 meters. Option two is to see the bridge and train passing from above. The coordinates are 46.680606, 9.673579 and its a 20min walk from the parking lot and 900 meter.