How hard is the drive from Innsbruck to Fussen?

There ARE some harrowing mountain passes in Germany and Austria... but the route from Innsbruck to Füssen is not one of them.

Mountains? I live in Colorado; we have mountains. Germany has hills. I took the train from Mittenwald to Seefeld, which is the top (just over 1200m or 4000 ft) of the "pass" between Innsbruck and Garmisch-Partenkirchen. It didn't look to me much more mountainous than the Adirondacks. I've also been over Brenner Pass (~4500 ft) from Innsbruck to Italy. The most "white-knuckle" thing about it is the highway, which is on stilts, often hundreds of feet above the valley floor. Here is another picture I took from the train on Brenner Pass near the "summit". If you are at all concerned, you can take the train from Innsbruck to Garmisch-Partenkirchen. From Ga-P there is a regular bus to Füssen.

The drive from Innsbruck to Füssen is like the drive from Denver to Vail. You keep wondering where the inclines are. There are none... You see the mountains but don't get to feel them. ;-)

The Fernpaß summit is "only" 1228m high. It's more like a hilly area than a major mountain pass like so many others in Austria, Italy etc. It's a well-traveled route offering no major challenges on summer and in all probability no snowfall altogether.

Hmmmmm, I think I'd be more white knuckled driving in New York City....lol...
The drive from Innsbruck to Fussen( I did it in a rental car in 2009) is actually quite enjoyable, scenic and winding roads, hilly but certainly not mountainous. You'll be fine....