3 nights in Germany - between Bruges and Frankfurt

Have you considered Aachen?

Würzburg and Rothenburg are both a bit out of your way. I would rather look for a location that is on the route from Bruges to Frankfurt. The most obvious destinations are the Middle Rhine Valley (Boppard, Oberwesel, Bacharach) or the Mosel (Trier, Cochem, etc.).

I am partial to the Mosel Valley, perhaps Cochem. Good biking there along the Mosel. Or perhaps Boppard on the Rhine. about 5 hours from Bruges by train. Boppard to Frankfurt airport on a direct train is 1 hour and 20 minutes.

"...envision training to Frankfurt on flight day."

I would want to be closer to FRA than Aachen, Cochem, Rothenburg, or Würzburg, myself. (These last two lie well beyond FRA airport anyway.) I might be weird about this, but I plan for the worst-case scenario on flight day. I try to overnight within one hour (but preferably less time) of the airport, and I plan the final trip to the airport only with trains that go directly to the airport from where I am staying. With connecting trains, there's always the soft promise of a missed connection... no thanks. Cochem may look close geographically to FRA, but it's at least 2.25 hours away and requires a connection or two.

MAINZ is a very good option. It's actually on the way to FRA from A'dam and there are multiple DIRECT trains per hour heading to FRA, with a travel time of only 20-25 minutes.

Mainz is not a big city, but it's not a small town, either. So maybe what you do is book your last night in Mainz and the first two of your three nights in Cochem, or in Boppard. Personally, I'd go with Boppard in your situation. It's a great town for outings on the Rhine because of its central location, and you can day trip from there to Cochem if you like. On your 3rd day, you can continue your sightseeing in the immediate area if you wish... play it by ear... and end your day at any hour you wish in MAINZ.

The other truly great thing about Boppard is the VRM Guest Ticket Program. All Boppard lodging guests receive a Guest ticket that provides free local bus and train travel for your outing to Cochem and other nearby destinations.

https://www.vrminfo.de/en/tickets/tickets/leisure-tickets/vrm-guest-ticket/

Since your going to Frankfurt, I’d spend 3 days somewhere near Koblenz. Pick a little town you like and set up base

It may not be close enough to Frankfurt, but I love Cologne. (More urban and art-oriented than Middle Rhine Valley.) We flew a two-segment flight NYC-Cologne for zero extra money. United/Lufthansa codeshare may have been a factor.

Although beyond FRA from Bruges, for practical reasons Wurzburg is a good choice. Rothenburg can be visited easily from Wurzburg. Veitshöchheim and Iphofen are close by.

Another very good option would be Eltville, an attractive small town not far from FRA ( 1 hour or so). You can hop on a ferry from here to visit some of the better known villages and towns on the Rhine, and Rudesheim is nearby.

Would Wurzburg be a good base for 3 nights?

In my opinion, yes. Three nights will give you a full day in Wurzburg, and a full day for a side trip to Rothenburg. Although not on a direct route from Bruges to Frankfurt, the train connections should be easy.

I would stay somewhere on the middle Rhein. I've been to Koblenz, Braubach (Marksburg), Boppard, St Goar, Oberwesel, and Bacharach, also Mainz. I've stayed in Boppard (5 nights) and St Goar (2 nights). St Goar is my favorite.

I plan the final trip to the airport only with trains that go directly
to the airport from where I am staying.

It doesn't look like there are direct trains from St Goar to the airport, but there are direct trains from St Goar to Mainz, and, as mentioned above, there are frequent trains and S-Bahn from Mainz to the airport.

One of the longest day-of-departure trips I've had to the airport was a direct RE from Boppard to the airport in 2004.

It doesn't look like there are direct trains from St Goar to the airport

But the RE 2 is direct from Boppard, Oberwesel, and Bingen Hbf.

It doesn't look like there are direct trains from St Goar to the airport
But the RE 2 is direct from Boppard, Oberwesel, and Bingen Hbf.

@Lee, Sam:

Please have another look at my post. I did not suggest a final train ride from St. Goar to FRA airport. I suggested splitting the 3 total nights into...

a) 2 nights in St. Goar (or in Boppard) and
b) 1 final night in MAINZ.

Staying in MAINZ on Night 3 results in a DIRECT train to FRA on departure day, and it turns both St. Goar AND Boppard into viable base town options for the OP's situation.

Wow - thanks to everyone for these wonderful suggestions. I love researching for a trip and have learned that personal insight can help me get on the right track quickly. I'm deep into my Rick Steves' books today looking into these recommended towns and areas. Thank you again!

"I'm deep into my Rick Steves' books today looking into these recommended towns and areas."

Together, Sam, Lee, sla019, and I have mentioned "Boppard" about 14 times on this page. Rick Steves mentions it most briefly in my copy of his book on Germany, but he assigns it no stars and provides no guidance at all for lodging or dining options and other details for staying there... My advice... Don't let Rick's silence on Boppard - or other places we recommended in this thread - dissuade you from researching them more thoroughly in other sources/guidebooks. Rick's materials for Germany tend to be less than comprehensive, as a rule.

A couple of links I happen to have handy for you...

Boppard:

https://www.boppard-tourismus.de/media/was-ist-wo-broschu__re_en_190218.pdf
https://www.boppard-tourismus.de/en/
https://www.tripadvisor.com/Attraction_Review-g198627-d3306006-Reviews-Sesselbahn_in_Boppard-Boppard_Rhineland_Palatinate.html

Braubach (mentioned by Lee; Rick is mostly mute on Braubach too:)

https://delveintoeurope.com/braubach-germany/

(3 pages of photos) https://www.stadtbild-deutschland.org/forum/index.php?thread/7322-braubach-am-rhein-und-marksburg-galerie/

Rick is mostly mute on Braubach too

Maybe that's because the Marksburg, in Braubach, is competition for his "favorite castle in all of Europe".

I've stayed in both Boppard and St Goar. I would prefer St Goar. Boppard is nice, but a little too big for my liking. Plus, the riverfront hotels seemed a little pricey when I was looking in 2004. I stayed in what the hosts called a Pension, but was really more like a Privatzimmer, a few block back from the river.

In 2004, I came into FRA on a direct RE from Boppard. My flight, as I remember, was in the early afternoon. For an earlier flight, I would travel to Mainz late in the day before, stay in Mainz (I like staying across the Bahnhofplatz from the Hbf in Mainz), and come in on the S-Bahn in the morning.

Great ideas. Thank you. I will research some of these other towns with other resources.

When staying "across the Bahnhofplatz from the Hbf in Mainz" - do you have a recommended accommodation? We'd be staying just one night with an 11:45am flight out of Frankfurt. Thanks again. I wish I could buy you all a drink! LOL

Lee has often recommended the Koenigshof at that Mainz location.

I've staid at the Schottenhof, across the street from the Koenigshof, a little less expensive for a one-nighter. There is also a Marriot there if you want high end or have points.

I am assuming that you do not have your bikes for this part of the trip, having used ones provided by the tour company on the barge.

Any of the towns between Koblenz and Mainz are fine. You could even stay in Limburg an der Lahn. With an 11:45 flight, I wouldn’t be too concerned about getting to FRA. Mainz is fine for the last night if you are nervous about making it to the airport. I’ve had no trouble leaving early from Bacharach for earlier flights

Consider Luxembourg and/or Trier.