Do you have any recommendations for my trip to Germany this summer?

The highlight is going to be visiting The Porsche museum in Stuttgart. I’ll have about a week, willing to drive or travel by train. I’d love to take a boat ride of some sort down a river one day through beautifully scenery, but I don’t have the time to do an actual river cruise from what I can tell from my research. They all seem to be 7+ days. If you know of a 3–4 day one that you recommend I would consider it.

My husband prefers green countryside, forests, and mountains to big cities, although I am interested in going to a good history museum, which I assume would be in a city.

I have an old school friend living in Berlin who I might try to see. We are only in touch by facebook at this point. But, i hear Berlin is fantastic.

Also, any particular very scenic roads would be great for a day of driving and touring on the way somewhere, but preferbly a road with faster speeds. My husband can only last at 40 mph for a short time.

Thanks!