Stop reading here, if you do not like to toture yourself by biking uphill a 1200 m altitude or riding small single-trails. As well stop reading here if you not like terrific views or ancient hidden Walser colonies.
In case you love all of that I recommend the following tour starting at Thusis in Graubünden right at the Viamala gorge, where the river Rhine (in Retoromania: Rein Posteriur) breaks through.
The small detour passing Carschenna helps to to avoid the national road where truck try to kill you.
As soon as you enter the small dirt road direction Mutten (there is a bus stop), you will shift in a small gear. 1000m giong uphill in 10km way are waiting for you. There is no chance of a rest or relieve other then to take a break in turning the wheels.
Obermutten is the place for a break. Obermutten is an acient Walser colonie hidden at the rim of near the col. You will see Obermutten in the last moment and it cannot be seen from the mountains around (I tested it). The Walser, moving from the Wallis direction east about 1200 a.d. wanted to live as free farmers and often settled in hidden places up the mountains. Now these colonies are recommended to be set under the UNESCO Convention Concerning the Protection of the World Cultural and Natural Heritage.
Then we left for starting with the downhill direction Sarnest and Zillis right before the Viamala gorge. The next image tells you how the beginning of this trail looks like.
...and yes, Gemsli was waiting for us.