Munich to Frankfurt after Christmas

I'd use the trains, then you don't have to worry about chains and ice and snow. Plenty of places to stop between Munich and Frankfurt in 1 week. Nuremberg, Bamberg, Wuerzburg, and Rick's fave, Rothenburg. Pretty much all in Bavaria, so you can use Bayern Tickets, or VGN Tagesticket Plus.

You will likely want to stick mostly to cities in winter as many of the smaller towns offer few if any wintertime diversions. Germany's efficient and extensive rail system will serve most people's needs more than adequately. The Romantic Road is okay and you may or may not want to visit some of the smaller towns, but in that general area, I think Sam's advice to visit Nuremberg, Würzburg (a RR city) and Bamberg, places where you'll find much more to see and do, is wise; Rothenburg, probably the most well-known RR town, can be a day trip by train from either Würzburg or Nuremberg if you wish to visit. Another RR city near Munich is Augsburg (also very easy to reach by train.)

Are you interested in visiting a German Christmas market? Not all close just before Christmas. The Speyer Christmas Market remains open through Jan. 6 (closed on Christmas and the 26th however, with limited hours on NYE and NY day.) Speyer is well known within Germany as an interesting destination on other grounds as well.

https://www.speyer.de/sv_speyer/en/Tourism/Tourist%20attractions/
https://www.speyer.de/sv_speyer/en/Tourism/Museums%20and%20Learning%20Places/
https://www.speyer.de/sv_speyer/en/Tourism/Speyer%20for%20.../...%20bathing%20beauties%20and%20aquarians/

Where is Speyer? Very close to Heidelberg and Mannheim. So an alternative route to consider might be Munich - Augsburg - Ulm - Esslingen - Stuttgart - Ludwigsburg (baroque palace) Speyer - Heidelberg - Mainz - FRA airport. (No problem doing such a route by train.) Besides Speyer, I suggest you investigate these other places to see what interests you most.

I like the suggestions above and add one more favorite: Regensburg.

https://mcchelsea.smugmug.com/Advent-2010/Regensburg/

I did not now about the Christmas Market at Speyer. Great news. We visited Speyer for the first time this spring and really enjoyed the atmosphere of the town. Its great cathedral is now one of our favorites for its simple beauty and power. There were two other beautiful Protestant churches as well, plus the haunting remains of a Jewish Ritual Bath.

Although I am a fan of Rothenburg, I understand that it buttons up after Christmas. I noticed that our favorite hotel takes a long vacation at that time.

Thank you-- those are great suggestions. We love old small cities, and are not big on 'nightclubs and sparkle' but love old castles, towns and local pubs. Open really to any itinerary for about our 11 days that starts in Munich and ends in FRA; (good flight deal). I will definitely look into the Bavarian Train. Will miss flexibilty and storage ability of a car, but am concerned with weather conditions that time of year.

"We love old small cities... love old castles, towns and local pubs."

Based on this I'd say that Bamberg (UNESCO World Heritage old town and beer mecca,) Würzburg (fortress, Residenz palace) Nuremberg (castle, attractive old-town zone, more) and Regensburg (UNESCO World Heritage old town) are very good suggestions for you. As cities go, Nuremberg is a larger one; however, once you're within its old-town zone, you'll likely think otherwise.

Here's a sample plan for getting to and around these places and for side trips:

Day 1: Munich (relax, recover from jet lag, see something minor.)

Day 2: Travel to Regensburg for full-day visit (use station locker for bags); travel in pm to Nuremberg for 4-5 nights.
(Here's where your flexibility and spontaneity come in... Do day trips as you feel the mood from Nuremberg to Bamberg, Rothenburg, Coburg fortress and explore Nuremberg as well.

Day 7: Travel to Würzburg for a full-day visit there (use station locker for bags; proceed to Heidelberg (lightly damaged in WW II) for 4 nights... Do day trips as you please to Speyer, Mainz (small but nice old town zone with a large pedestrians-only sector, Ludwigsburg, Bad Wimpfen, and Ladenburg

From Heidelberg you can travel easily to FRA airport for your departure.

Between Munich and Rothenberg is Nordlingin; one of my favorite towns in the area. The old town sits in a natural crater caused by a meteor impact, and that was the "city wall" in medieval times. Very few tourists, and fewer still know the geologic history.

My sister in law fell in love with Nuremberg on her first visit (3 years ago). In December it's very beautiful and easy to get around. The Christmas market is one of the best anywhere, and while it will be closed after Christmas, the normal open air market in the main square will still be open (although reduced).

Bad Windsheim is another often overlooked town with a lot of appeal, and Ansbach is great to walk around when the days are short and the tourists are gone. If you want small towns these are going to be more your style (okay, Nuremberg is big) than Bamberg or Wurzberg. Frankly, Bamberg (which I like) is out of your way.

If you're still traveling on New Years Rothenberg always has a big fireworks display New Years Eve. Back when I lived there we'd drive over and sit on the hill outside the town and share a drink while the fireworks lit up the valley.

"Frankly, Bamberg (which I like) is out of your way."

With Nuremberg as a travel base, Bamberg is the closest of the day trips I suggested above - just 45 minutes by direct train.
Coburg is 70 minutes.
Rothenburg is 1.25 - 1.75 hours.

Nördlingen is a very handsome RR town populated by everyday folks and with fewer tourists than Rothenburg. I've never been there in winter. But it's only about 1 hour by train from Augsburg if you happen to end up staying in Augsburg.

Bad Windsheim is nice enough too and its best attraction - the open air museum - is outstanding. But like many attractions in Germany's smaller towns, it's closed in January :(

You all are AMAZING!! Christmas markets had been on my desired list, but thought they would all be over. Now to make the big decisions. There will be three of us, so it will fun. Thank you for all the help!