Highlights: Thun (& Castle)
Route 99: Section 4 (Thun 560–Langnau I.E 670)
Stats from SwitzerlandMobility.ch (https://www.schweizmobil.ch/en/cycling-in-switzerland/routes/route/etappe-01073.html): 67km long, height difference Thun–Langnau 1,800m (1,650m in the opposite direction). Their site has the full profile. The highest point is 1,137m.
Sept 2018
I haven’t biked in over a month and I was a bit uncertain if doing this tough Section, but the weather was great and I wanted to put in one last long ride above 1,000m before the fall set in. This is also an ideal route for a cloudless day because of incredible views of Lake Thun and the Alps.
Overall, the section goes through very quiet roads, in a rollercoaster of uphills and downhills, alternating between forests and scenic hills.
I biked in the opposite direction, skipping the first few kilometers, already covered in 99:05, and starting directly from Signau (total 68km).
From Signau, the road starts with the gentle landscape of the Emmental region and then flows into the forests of Eriz. 
The many hills made me use more battery than I expected so I decided to stop half-way at an official Heartroute e-bike recharging station. The place was very convenient, right along the route, and equipped with drinks and a picnic table where I snacked while recharging a little.
Towards the end, the route opens to particularly beautiful views of the entire Lake Thun and of the Alps in the background.
It then goes into a wonderful descent all the way to the picturesque town of Thun and its landmark fairytale castle.
In Thun, the warm weather brought people to its Aare river for bathing, floating, and surfing right in town!
Thun is a crossroad for several cycling routes, among which are 99:03 , 8:03 and 4:06.
Links to Introduction and other Sections:
bikeswitzerlandblog 
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