Help with December Itinerary

not insane but can be tidied up.

14-16 Baden-Baden is not brilliantly placed for getting into the Black Forest.
17 Strasbourg, I can understand the day visit but is there a reason for an overnight? Strasbourg is less than 30 minutes by local train from Offenburg.

Neither Offenburg or Baden-Baden give visitors the Konus free travel card for the Black Forest region. Put all 4 nights into one Konus location near to Offenburg with a good connection to the Strasbourg train and you can maximise time and minimise hassle. Gengenbach appears to be this weeks favourite with forum members and there you do get the travel card (you need to pay a little extra from the border into Strasbourg). Depart Gengenbach 8:53, change at Offenburg, arrive Strasbourg 9:34 - hardly worth repacking for!

http://www.gengenbach.info/

http://www.blackforest-tourism.com/info/KONUS

Gengenbach - Stuttgart, depart 9:12, change at Freundenstadt arrive Stuttgart 11:42 - free as far as Eutingen (buy onward ticket at Gengenbach as you won't be getting off the train at Eutingen).

20 Nuremburg. Fast train every 2 hours from Stuttgart taking just over 2 hours. Book in advance for good savings - reservations beyond 9. December not open yet! Also book Frankfurt - Gengenbach when you do this.

Nuremburg- Fussen, Fussen-Salzburg and Salzburg-Munich (assuming you need to go beyond the main station area in Munich) should be made on the Bayern Ticket day passes for €31 for two people (I assume we = two) bought on the day.

....and this may be useful

http://www.weihnachtsmaerkte-in-deutschland.de/

Both Nürnberg to Füssen and Füssen to Salzburg are time consuming trips. And with unfavourable weather conditions, Füssen / Neuschwanstein might dissapoint you. You might consider going to Garmisch or Mittenwald instead, with an intermediate stop in Oberammergau / Ettal and a side trip to Linderhof.

I'm generally a fan of Gengenbach and the Black Forest, but your plans there for December - 14-16 Baden Baden and Blackforest(3 nights) will probably not be especially fruitful as the smaller Black Forest towns tend to be shuttered and somewhat like ghost-towns. Baden-Baden's focus on casinos and health spas is strong, if that's what you intend there, but there might be better places for indulging your stated interests in "...scenic views, Christmas markets, some castles..."

After landing at FRA, I'd be tempted to ride the direct train to Mainz am Rhein (25 minutes from FRA) for a few nights instead. Mainz has a large and lively Christmas market, lots of hotel and restaurant choices, and is a great place to visit anyway.

https://www.youtube.com/watch?v=Vf_0UKNq90w
https://www.tripadvisor.com/Attractions-g187393-Activities-Mainz_Rhineland_Palatinate.html

Mainz is a good base for a day trip or two. Castles? There are 40 of them in a 40-mile stretch of river north of Mainz. Map w/ links:
http://www.loreley-info.com/eng/rhein-rhine/castles.php

Marksburg in Braubach is an intact medieval castle open year-round for tours:
http://www.marksburg.de/en/

You can take a train down one side of the river and up the other between Mainz and Koblenz. Once you reach Bingen the scenery gets intense:

https://www.uli-franke.de/wp-content/uploads/2014/07/20140622_144833-Burg-Rheinstein.jpg
https://upload.wikimedia.org/wikipedia/commons/e/e3/Maeuseturm_Burg_Ehrenfels_Bingen_Rhein.jpg

The Rhine scenery in winter is not lush and green - stark, but still impressive. The railways hug the river bank - views are best looking across the river, so it's good to ride along both riverbanks.

http://media.gettyimages.com/photos/winter-in-bacharach-at-the-river-rhine-middle-rhine-rhineland-in-picture-id550647671
https://deeleea.com/wp-content/uploads/EUR2016-0013935.jpg

If the weather is OK, stop off in one or two towns for 1-2 hours for a walk around just to check out the old town walls and half-timbered buildings. Don't expect the towns to be lively though.

Bacharach: https://upload.wikimedia.org/wikipedia/commons/4/4c/Bacharach_BW_9.JPG
Oberwesel: http://www.oberwesel.de/en/wandern0/stadtmauerrundweg/

Rüdesheim could be a stop on this outing or done as a separate outing from Mainz. The Christmas market in this old-world wine town is very popular and for good reason.

http://w-d-n.de/en/

My daughter and I spent a couple of nights in Mainz a few years ago and very much enjoyed both the Mainz and R'heim markets, as well as the Trier Christmas market. Trier is on the border near Luxembourg and also a very worthwhile city. However, it's a long train trip from Mainz and probably for this reason not to be recommended unless your time is ample.

http://www.trierer-weihnachtsmarkt.de/en/
http://www.trier-info.de/english/sights-in-trier

Strasbourg's Christmas market is a biggie, and Strasbourg can in fact be reached in 1.3 hours from Stuttgart (rather than from Baden-Baden.)

Your route is completely doable by train, btw.

Have a look at the German Rail Twin Pass, often a good deal for couples. The GRP by the way also serves STRASBOURG (on the Mannheim-Strasbourg route anyway) and SALZBURG despite their locations outside Germany.

https://www.bahn.com/en/view/mdb/bahnintern/international/partnerbilder/pdf_2017/mdb_242383_flyer_grp_2017.pdf