>> On Google Streetview the location from which you can see the view is described as Aussichtsplattform Landwasserviadukt. Have you been there or have any idea how you get there? Is it a hike out of Filisur?
I didn't know about it before your post! So I haven't been there. However, I have done a little research :-)
It appears you can hike there from Filisur Station. The track doesn't seem to be too difficult, but there is a short, steep section. You can also retrace your steps to the path junction to continue down to the riverbed and walk underneath the viaduct.
There are also apparently another two viewpoints on the other side of the tracks that look straight onto the tunnel entrance (which does not seem to be visible from the viewpoint closer to Filisur). People seem to get to the other viewpoints from Schmitten, and say it is a demanding, very steep 30-minute hike, requiring reasonable fitness and sure-footedness; not well signposted; proper hiking shoes should be worn; drinking water should be taken.
>> When heading north do you get any sightings of the viaduct from the train prior to popping out of the tunnel?
I wouldn't think so, due to the height of the mountain through which the tunnel goes. Also there are a lot of viaducts that look similar, and without the iconic view of the tunnel into the rockface at the immediate end of the viaduct, you can never be really sure which viaduct you are looking at. On one occasion when I was travelling towards Chur on a regional train, although I had a window seat on the left and was looking out of the window the whole time, I never was sure which of the many viaducts was the Landwasser!
>> When heading south I can't remember whether I ever looked back after going through the tunnel to see if I'd get another view from further down the track. I don't think I did.
Probably not! There is so much else to see just looking ahead!
I have attached a map and an aerial view showing the hiking trails around the Landwasser Viadukt, including the one to the viewpoint you found.
Here is a summary of pertinent information I found about the hike from Filisur station and photographing trains on the viaduct (a lot of which was in German):
---Hiking time from Filisur station: 15-60 minutes (varies according to different people!)
---Be aware of the train times (both ways) if you want to photograph a train on the viaduct
---The trains heading towards Chur come out of the tunnel very suddenly, and you have to be quick to snap them before they whiz across the "best" part of the viaduct.
---You have more chance to be prepared with your camera with trains heading towards St. Moritz
---Afternoon or evening is best, as trains are in shadow in the morning
The most useful directions I found for the hike are in the post titled Great walks to view Landwasser Viaduct on the following Trip Advisor page:
The site my screenshots come from is:
(Thanks to Slowpoke, from whom I first learned about this site, and how to turn the hiking trails layer on!)