Alsace Region

I would check out Colmar, especially if you're a foodie like me! https://www.rome2rio.com/guides/5-french-towns-you-need-to-visit/

Colmar is a very nice small city.

If you are at all into road or rail transport, the French national car and railway museums at Mulhouse are both world-class.

3 days isn't much for Alsace, but since it's what you have . . . There's Strasbourg, worth a full day minimum, don't miss the cathedral. The Folk Museum is excellent. Colmar is charming, again worth a full day. From Colmar you can visit nearby villages though they may be pretty closed down, but preparing for the Christmas markets. I just looked at this official site and it seems some of the markets will open in November.

There's good train service between Strasbourg and Colmar. For the villages, you need to use the local buses from Colmar or rent a car.

You probably stop in Strasbourg and/or Colmar on the cruise, do you not?

I believe it stops in Strasbourg

Without a car, Colmar is probably your best bet. It's too big for my tastes as a base but it is an attractive town, and is handy for public transportation to EuroAirport and to the most often visited villages - Riquewihr, Ribeauvillé, Kaysersberg and Eguisheim.

Riquewihr is a pretty, busy village. If you can handle a moderately difficult hike, from here you can walk to Hunawihr, onto Ribeauvillé (three castle ruins) then further afield on to the undervisited Bergheim. Bus back. Walk to and from Kaysersberg via two separate routes.

As mentioned above, Mulhouse may tickle your fancy if you have a keen interest in cars and trains. It is not an attractive town.

Our river cruise out of Basel stoped in Strasbourg and also had an optional excursion to Colmar.