Ideas for a post Danube cruise 1 week tour

It's probably going to be hot. Keep in mind many places to stay will not have air conditioning. Mountains and lakes would be my recommendation. Better yet, lakes in the mountains.

My sister and her husband spent a week in Salzburg. He wants to go back for a month !

Start with a stop through Munich? It's right there. Nice trip for sure from there into Northern Italy, and surprisingly quick by train.

There is plenty to see near Regensburg where your cruise ends.
Places to take in are Nuremberg, Prague, Munich, Salzburg, Berchtesgaden and Garmisch/Fussen.
Or head toward Dresden and Berlin.

End of August is the start of fall. The heat wave is mid-July so I wouldn't sweat it.

Heat is relative to what you are use to. I just plugged in a few of the cities mentioned and a few US (dont know where you live) and it looks like "typically" you would be hard pressed to find yourself in temps over 80F.

https://weatherspark.com/compare/s/1/81358~77807~73308~8813~1705~23912/Comparison-of-the-Average-Summer-Weather-in-Vienna-Prague-Regensburg-Dallas-Los-Angeles-and-New-York-City

Otherwise I would suggest, first, most of the River Boats do a short and not very impressive tour of Budapest, so that deserves another day.

Then I would be tempted, at the end, to go to Cesky Kurmlov then visit a castle or two on the way up to Prague. Sort of fits the theme of the trip and its a beautiful trip.

Regensburg is just 75 miles northeast of Munich. I'd start there and then rent a car making a circle thru Bavaria and Tyrol region of Austria. It's a great place of incredible beauty.

Then you could fly out of Munich.

Dropping a rental car in another country is just too expensive with drop off fees.

After more research, I’ve booked a flight to Prague three days in advance of our river cruise. We will spend 1 1/2 days there before taking the train to Budapest. After the cruise, we plan 2 days in Munich. We fly home 6 days later from Geneva. We’re thinking 2 days around Innsbruck then 2 days at a stop still to be determined before spending the last two nights in Geneva. Trying to decide between Zermatt, Lucerne or Milan. Thoughts on the itinerary?

Like it!

If me, I'd roll Innsbruck into Lucerne and park it for 4 nights in Lucerne. If i wanted to bias a bit more to the towering and glaciated while still having some agriculture elevation time, then Wengen in the Berner Oberland for 4 nights.

Or if i was interested in spending less, I'd do 2-3 nights in Shruns Austria, Ernest Hemingway's preferred alpine village, and then a couple of nights near the Rhinefalls and explore than area a little.

But your plan is just fine too.

Prague to Budapest by air is 4 hours faster door to door than the trains. The flight itself is 1:10 vs about 7:10 hours on the train. Depending on how you pack it can be fairly cheap. But check a bag and figure 1.5 times these rates:

Sunday about 9pm ……… $97 Ryan
Monday about 7pm …… $56 Ryan
Tuesday about 6am and 6pm ……. $50/$56 Ryan
Wednesday about 6pm …….. $48 Ryan
Thursday and Friday about 8am …….. $85 Ryan (Here, I looked this one up: goes up to $116 with a full size carry-on and $126 with a checked bag and $175 with the full size carry-on and a checked bag).
Saturday Nada

https://community.ricksteves.com/travel-forum/czech/prague-to-budapest-transportation-options (there is an error, the 4:45 really adds up to 4:15).