2 days before or after a weeklong bike and barge trip Aschaffeburg to Bamberg?

I would opt for Bamberg over Frankfurt. There are several other interesting towns near Bamberg such as Nuremburg and Coburg.

Depending on your interests, use of car or (excellent German) train, and your flight out city, have a look at this Trip Report. Maybe search for "Aschaffenburg" and then look at the paragraphs nearby. Although Aschaffenburg is my first choice, Frankfurt has enough for two days with only very local bus or train to nearby (for example, Fachwerkstraße) towns. But it's a "big city visit." I think you are too early for regional Wine Festivals, but you might check on dates.

https://community.ricksteves.com/travel-forum/trip-reports/baltic-germany-fachwerke-landesgartenschau

Note that I am not pretending to be a regional expert, just reporting on what we did. I have not been to Bamberg, but I am interested in nearby Bayreuth and the opera house. Despite your boating, the scenic Middle Rhine (Bingen to Bachrach, say, by dayboat) is easily accessible from Frankfurt. Search box top center, "middle rhine". Are you aware Rothenburg ob der Tauber is so popular on this board that it's referred to as RoT?

If we fly into Frankfurt am Main, we almost always spend the first day or two in Aschaffenburg. It is not a major tourist destination. It has an Archbishops Residenz with its gardens, a museum and a nice river front. Aschaffenburg also has a a very old Abbey Church (Kollegiatstift St. Peter -957 a.d.)

For us it is mainly a pleasant shopping area, good restaurants and a chance to recover from the flight over.

Wikipedia does a decent job with Aschaffenburg.

We generally like history and smaller towns. Any suggestions would be appreciated.

You can visit SEVERAL truly small, historic towns that line up neatly in a north/south orientation just to the south of Frankfurt... This flyer provides info as well as a map of all the train stops for this area, known as the Bergstrasse:

https://www.diebergstrasse.de/holiday-route-bergstrasse/

Milk-run RB trains that stop in nearly every small town between Darmstadt and Heidelberg leave Frankfurt's main station at :06 after every hour; faster regional express trains that skip certain small towns also serve this route.

Aschaffenburg would be a good choice. There is a nice castle, a couple of good parks, Pompejum and several good places ot eat. One can also do a day trip to Mespelbrunn (a fairy tale castle with a moat), Heidelberg, or Miltenberg. Do a google search and see if it holds any interest.

Thank you all for some great suggestions- there are more options than I realized. I wish we had more than a couple extra days but that will have to wait for another time. We will probably try the train route this time since there seems to be a good network in this area.

Carol, where does your tour end?

The tour starts in Aschaffeburg and ends in Bamberg on a Saturday morning. Either Bamberg or taking the train over to Nuremberg sounds appealing, don't have time for both. We'll probably have to fly into Frankfurt and out of either Frankfurt or Stuttgart on that Monday (cost is the same). So we'll only have a couple days- family obligations.

Why Bamberg? There are a lot of really nice towns closer than that. Mainz, Bad Homburg, Bad Kreuznach, Worms, Speyer, Neustadt on the Weinstraße, etc. And those are really easy to reach by train. Limberg, Cochem, Mannheim, Heidelberg, those are closer than Bamberg, and just as nice. Don't get me wrong, I like Bamberg, but when you're on vacation every hour you spend getting somewhere counts against time you could be somewhere else and actually doing something.

Why Bamberg?

Good question. I would also ask Why Nuremberg? I like both of these cities very much. But neither Bamberg nor Nuremberg meets your "small towns" criterion.

The reason for Bamberg is that the bike and barge tour actually ends in Bamberg so we're already there. Since I only have 2 days max to do anything else, I don't want to spend any more time than necessary traveling. I was trying to find something close enough to the finish of our tour and still be close enough to get to the airport so as not to waste any time. The barge tour is already committed to.

...tour starts in Aschaffeburg...probably have to fly into Frankfurt and out of either Frankfurt or Stuttgart...

That being the case, Aschaffenburg is a quick, direct train ride from the main rail station in Frankfurt. Don't think you can go straight from the airport, but it's easy to go from the airport to the main station. Going a couple of days early and staying in A'burg will be advantagous for two reasons. It will give you time to get over any jet lag, and it will keep you from missing the boat if there are flight delays. If you do stay in A'burg, we can recommend the Hotel Post which has a good restaurant, or the Hotel Wildermann that also has a good restaurant. Flying back from Stuttgart will eliminate time lost backtracking to Frankfurt. Enjoy my old stomping grounds for me!

If you are leaving Frankfurt or Stuttgart on a Monday morning, taking into account travel time you really only have one full day to spend wherever you choose, plus some of an afternoon and evening.

Aschaffenburg is on the way to FRA (1.5 hours), and Selingenstadt close by has a nice, small old town.

My first choice would be a slightly longer train ride to Eltville, which is only a 0.5 ride from FRA. Eltville is a pretty little place, Kloster Eberbach just up the hill, Rudesheim and its attractions a short journey away.

Thanks to all that have replied. We have plenty of information (a bit overwhelming) now to come up with a plan and are looking over our options. No matter what we decide, I'm sure it will be interesting to visit the area. Thanks again

There is now a direct train from the Frankfurt Airport to Aschaffenburg. HLB RB58

https://int.bahn.de/en/offers