7 days itinerary around Frankfurt

You can fit in Tuebingen.

I have to disagree with Ashley; I would much rather use Gengenbach as a base for exploration of Baden-Württemberg. There doesn't have to be a lot to see in the town you use as a base, it's not a destination, just a nice, relaxing place to return to each night.

In 2008, I spent a few days in the little spa town of Bad Herrenalb, a lovely base, with its own Therme (spa), just 38 minutes from Karlsruhe Hbf by streetcar. I've used it as a base for day trips to Bad Wildbad - another great little spa town - Baden-Baden, Calw, Karlsruhe, and just to tour the Black Forest. Baden-Baden was just over an hour by direct bus. I did not like Baden-Baden. To me it was too big and industrial. One of the big attractions is an overly glitzy pedestrian shopping street; shopping is not my thing. The best part of Baden-Baden to me was leaving.

BTW, pay attention to the spelling of German towns. There are a lot of towns in Germany with similar (or the same) names. You don't want to go to the wrong one. Gengenbach is spelled with an 'h', not a 'k'. (There is no town called Gengenback, so you are probably safe there, but in the case of Freiburg, there is another town, near Dresden in Saxony, called Freiberg. You probably don't want to go there.

I don’t consider the BF to be “around Frankfurt.” But if you have looked up the train times, it is naturally up to you. I think big cities and museums are better targets in the dead of winter. Cologne is also a bit far, but we got a second segment to Cologne on a single ticket from Lufthansa for virually nothing extra. Duesseldorf would be just as good, and it’s the second biggest airport in Germany.

Why not go to Berlin or Dresden or Leipzig?

Or look at some of the incredible villages and towns right around Frankfurt, and Frankfurt itself. You might love the "new" Altstadt, especially if you look up.

I don’t consider the BF to be “around Frankfurt.”

And Berlin, Dresden, and Leipzig are? Maybe you need to look at a map. Gengenbach is a little over 2 hrs from FRA. Bad Herrenalb is less than 2 hrs from FRA.

A few years ago, just after Christmas, while staying in Bad Herrenalb, we took the bus and train up to Freudenstadt. It was beautiful in the snow.

Thank you all for the suggestions. I did some more research and decided that we will be saving these places for summer vacation. Instead we will be going to Frankfurt, Stuttgart and Nuremberg during the 7 days. If there are places you think I should visit that are close to these cities, please feel free to share. Thanks again!

Near Frankfurt is the Hessen Park Open Air Museum that is open 7 days a week starting 1 March as is the Saalburg. Both are right outside of Bad Homburg.
https://www.hessenpark.de/en/hessenpark/
http://www.saalburgmuseum.de/english/museum_en.html

Heidelberg is an easy train ride from Frankfurt.
Other towns to visit would be Eltville on the Rhein along with Eberbach Monastery, Limburg, Marburg, Büdingen, Gelnhausen, Seligenstadt, Idstein as well as Mainz.

The Luminale will be in Frankfurt from 12-15 March in conjunction with a large trade fair. This will make hotel rooms expensive, but the Luminale itself is well worth seeing.
https://luminale-frankfurt.de/en/startpage/

Esslingen, Waiblingen, Bad Cannstatt.