Need your help finishing Itinerary in southern Germany

"Traditional Bavarian Germany" - not sure what this means. Old-world Germany is still visible in many places, but not so much in some of the places you mention. Munich, Cologne... hard hit. Konstanz? Spared. So maybe that's why it was a tip. Ask his friend about it? Rothenburg was around 40% bombed out and built back. Neuschwanstein was built in the era of the first skyscrapers! Hardly traditional Germany!

FRANCONIA (region that is mostly in Bavaria that includes Rothenburg) is on the way north and where you should find lots of old-Germany... Franconia has more beer breweries per square mile than anywhere in the world.

https://images.mygermancity.com/maps/franconia.png

Drive the Franconian branch of the Timber-framed House route. Lots of towns there to check out.

https://www.deutsche-fachwerkstrasse.de/en/Routes_Cities/Franconia.html

Bamberg has an old-town zone from the Middle Ages with UNESCO World Heritage status.

Also not far from Rothenburg is Bad Windsheim. Fantastic collection of historic buildings at the Freilandmuseum there. Place has its own brewery and period restaurants too:

https://www.tripadvisor.com/Attraction_Review-g198421-d284746-Reviews-Frankonian_Open_Air_Museum-Bad_Windsheim_Middle_Franconia_Franconia_Bavaria.html

Many other areas of Germany have similar architecture. You mentioned the Rhine...

Old-world towns on the Rhine south of Koblenz: Oberwesel, Bacharach, Braubach (which is the home of Marksburg Castle, also a true castle from the Middle Ages.)

Braubach - 3 pages of photos!

Marksburg

It sounds like a great trip! If you are interested in the Black Forest, one suggestion would be staying in Gengenbach. I stayed there for 4 nights in 2022 and absolutely loved it. The town is very charming with beautiful half-timbered houses (it's frequently called a "chocolate box" village) and has a beautiful Altstadt, with quite a few restaurants and cafes to choose from. Gengenbach makes a good base as it is right on the main train line, and gives you the options of some interesting day trips, including taking a day trip to Strasbourg, France, which is a quick 40 minute train ride away.

The town church (Saint Marion) is quite beautiful, and the medieval gates to the city are really interesting. The Benedictine Abbey is also worth a visit, and behind it are some cloistered gardens that were a joy to wander through. This was one of my favorite places. It was peaceful and inviting and I could have stayed for hours. There were little signs of inspiration scattered around, and some children from a nearby kindergarten playing on one side.

Also don't miss a walk through Engelgasse and Höllengasse streets (near the TIC). Here you will find cobblestones and half-timbered houses, flower pots and cats resting on doormats and quaint dolls in the window. I felt like I had walked back in time when I strolled through these quaint and narrow streets. There is also a nice hike you can take that will get you above the town with some absolutely beautiful views of below. The hike ends up at a church called St. Jakob auf dem Bergle that sits above town. The TIC in town will have maps showing you how to get there. it was a really nice hike and as I said, the views are just lovely!

One nice benefit if you stay in Gengenbach is that you receive a KONUS card, which entitles you to free public transport throughout the Black Forest region. There are many charming villages in the region that you can visit along the Black Forest Railway, and there is also the Vogtsbauernhof (open-air museum) that is a joy to visit and easily accessible by train. I know you said you have a car, but there's something iconic about taking a train through the Black Forest train routes. https://www.blackforestgermany.com/train.php

For what it's worth, Konstanz is quite beautiful but I definitely think you would find more to do in the Black Forest area.

Does it have to be Germany? What you describe is easily found in Salzburg, Austria and the surrounding lake region. If you’re envisioning cute chalets, beautiful mountains and lakes, cobble stone streets, great food and beer, lots of hiking opportunities, you’ll find it all in that area.

Cologne will probably be a disappointment. It was heavily bombed in the war and not much old-world charm remains. It’s a modern, bustling city.

Thank you so much for the thoughtful responses. A few answers to your questions....

Has to be Germany. I am going for business in Cologne and Germany is one of his top bucket list trips. Starting in Munich because of flight costs. I thought about Salzburg also but I think it will have to be another trip.

I stated "traditional Germany" and maybe should have said "American-ized expectation of what Germany looks like". When I ask him to describe what he is excited to see, he is describing Bavaria IMO. I do have mixed emotions about Neuschwanstein & will let him decide. Same for Rothenburg and the Schneeballs but I think he will enjoy the medieval aspect of it & with Rick's enthusiasm about it I decided to include it.

Agree with the Cologne sentiments - not spending any significant time there.

Your comments on Konstanz confirm what I was feeling - more of a resort town. I sent a similar set of questions to his friend but wanted to do my own recon amongst my Rick Steves peeps. :-)

Thanks again!

An Alternative to Konstanz might be Meersburg on the opposite side of Lake Constance.
There is a Car Ferry to Konstanz from there.(30min)
Meersburg is a 2 hrs drive from Füssen through the Allgäu region and along the Lake

You can visit the Meersburg Castle and the historic town and/or do a boatrip on the Lake to Konstanz and/or Mainau Island

Konstanz to Rothenberg makes no sense, especially from Munich. RodT is North of Munich; Konstanz is West and on the other side of the country (right on the border with Switzerland and Austria).

From Munich go to Rothenberg. While you're in the area go about 20 minutes drive to Bad Windsheim, where you can visit the very traditional open air museum, and (since you're into wellness) visit the Kurhaus (spa).

At that point it really depends on how many days you have before you have to be in Koln. If time is short head to Wurzburg, and then to Mainz, both of which are very nice cities to visit. if you have 4-5 days then head to Konstanz, and from there you can head north to Mainz on the Rhine.

Things to do in Konstanz? Zeppelin rides over the lake. Take the cable car from Dornbirn up the mountain and hike the Austrian Alps. Visit Lindau and/or Mainau. Tour Meersburg castle. Take a ferry ride. See the paleontology museum in Bodman. Visit the Rhine Falls. Drive over to Lichtenstein. Tour old Konstanz. There's more, but how much time do you have?

Konstanz is not really a resort city imho, but it is not really Bavarian (just like most largish cities tbh) - or what is a resort city to you?
More generally speaking, the lake it lies on is quite large, and allows for things like cruises, medieval towns, beer/wine, food, several spas (most towns there have one), etc. - I lived there for some time. Some larger castles are doable from there, like Hohenzollern castles in Bisingen or Sigmaringen. Smaller castle in Meersburg and others are closer. If staying there, you might prefer Meersburg or Überlingen, which are a bit smaller - more similar to Rothenburg, but with less American and more European tourists. Or Lindau on the eastern end of the lake (but I don’t know it well).
As to what to prefer, Black Forest or Lake: What do you like better? Woods or water? And not unimportantly, at what time of the year are you going?

Month and Year of trip? Total number of nights in Germany?

Konstanz is nice enough, and I think you are excluding the superior "scenic Middle Rhine" because it is not so far south. But if you are going to Cologne, you are passing it right by. Use the Search box top left to read hundreds of posts on the Middle Rhine.

Have you used Google Maps to list the miles you plan to drive each day, and added 15% to the Google time estimates? This short (?) trip has too much driving in it. You may be over-imagining the scenic things you are going to see from the highway. And when you do see a historic marker, it will take 15 minutes minimum, each way, to get into town, park, and get to the "attraction."

The Black Forest is also nice enough, but an outlier for time and miles. I wonder if the bath cities have an older idea of Wellness Culture than you two do? Is one of you someone who loves being behind the wheel?