<<"We will thus stay for 1 night in Davos and 3 nights in Wengen. What do you think of this itinerary?">>
I think it stinks.
The reason is a bit of prior knowlege. In 1997 we decided to spend some time in that region of Switzerland. There is a lot of history dating back to the middle ages, and there were trade routes from Rome up to the northern European countries/baronies/bishoprics/etc.
So, we assembled a list of objectives:
The 7th century church of St. Martin in Zillis;
The Preda to Bergun rail-trail;
Exploration around Tiefencastel;
The Landwasser viaduct;
The Via Mala,
and some other odds and ends.
Of all of them, the most disappointing was the Landwasser viaduct.
I will attach a picture in this post or an edit showing why.
You cannot get close to the tracks. You can look up. When you look up you can see the bottom of what you are looking at.
There are a lot of trees obscuring the sightlines.
Spend some time with on-line images of the viaduct. All the good ones are taken from a viewpoint at or above the level of the tracks. How do you get there? We could not find trails easily; possibly , permissions are needed. The only way you can do it is with a helicopter or with a drone. Or access through the properties above the tunnel. Maybe a very long lens.
Look carefully at all of the images and dimensions of the Landwasser viaduct on the internet. It is a small structure. Compare with the more approachable and larger Luogelkin Viaduct (or, the Bietschtal Brücke) on the BLS Südrampe trail between Hohtenn and Ausserberg.
So, your itinerary - basically, you have added a day of travel to visit a sight that you cannot easily see, even after you walk in from the road for about 3/4 km (you'll need a car) or from any place that you can reach.
The region around the Jungfrau is full of magnificent scenery in every direction. Spend your time there....you could spend weeks. Take a break - stay in the same hotel three nights in a row.
If you want to see rail engineering, start on the BLS Südrampe Trail.
Moredetails to be added in edit in a few minutes