As one of the last rides this year we decided to go to the Danube Valley (Donautal). The Danube Valley is known for it’s beautiful scenery and rock formations. The area between Zwiefalten and the Danube Valley is one of my favorite areas for finding beautiful narrow roads that are also well suited for rides on busy days, because they are usually rarely used.
The ride is ~150km long and takes about 2.5-3 hours.
Link: Kurviger
I attached .kurviger and .gpx files.
zwiefalten-danube.gpx (245.6 KB)
zwiefalten-danube.kurviger (17.4 KB)
At WP1 is the “Berghaus Knopfmacher” which serves as a good stop with beautiful views and good food. You should definitely walk the ~50m to the view point. Trained enduro riders might be able to make it down to the viewpoint with their bikes 
The start at Zwiefalten is perfectly suited to include a ride through the Lauter Valley (see this route: From Neckartal to the Großes Lautertal, Schwäbische Alb).
The pass from Thiergarten to Stetten is probably my favorite pass of the Swabian Jura. Unfortunately, they put up a speed limit of 60 recently, but it’s still a highly recommended ride.
Most parts of this ride are on narrow roads (paved tracks). There are some longer higher speed curves, but mostly narrow roads and curves.
If you are traveling, the area around Zwiefalten would be a good spot, there is a monastery brewery in Zwiefalten. There is also a very lovely smaller brewery in Zwiefaltendorf. It’s not recommended to continue riding after visiting a brewery
Below you can find a couple of pictures from the ride.
