Fussen to Rothenburg ob der Tauber to Nuremberg via train

You can use the bahn site for rail schedules, but don't pre-purchase tickets (they're non-refundable.) Just buy them at a station ticket machine on the day of travel or on the DB app.

https://reiseauskunft.bahn.de/bin/query.exe/en

Click on "only local transport" when you search. This will bring up trains that are usable with the tickets named below.

It's tricky to provide specifics without travel dates and the number of passengers / ages. Füssen or Fuessen is your start station. Trip will take 5.5 hours on 3-4 different trains, possibly a bus as well if you are traveling during a period of construction.. The Bayern Ticket day pass (€36 at the station for two adults) is what you need if "we" means a couple. Travel after 9 am on weekdays or at any hour on Sat or Sun with this ticket.

R'burg > Nuremberg: Buy the Tagesticket Plus day pass (€23) from a R'burg ticket machine. It's good for two adults at any hour on any day of the week. Trip takes less than 2 hours.

(Stephanskirche is the name of a church. You can input place names like that to pull up bus connections that you might need to use to get to the Füssen train station to begin your train ride.)

When I’ve gone to int.bahn.de site and typed in Fussen, it offers
Stephanskircher, Fussen but that doesn’t seem to be correct.

No, it's not correct. Stephanskirchen (with an -en) is a town just east of Rosenheim, and Fussen is a point of interest, street, intersection, ?, 1.8km from the Grasweg bus stop in Stephenskirchen. The Bahn website gave you that location because you typed in "Fussen" instead of "Füssen" (the town near the castles). Umlauts, those two little dots over the vowel, do matter. They're not ornaments. Ü is not the same vowel as U.

The old Bahn website used to have what I called an "ignorance algorithm", which guessed what you might want and gave people who typed in Fussen, Füssen, as an option. It is permissible to use the -e form for umlauts, i.e., ue for ü, on the Bahn website. Try it again as "Fuessen", and select "Bahnhof, Füssen" from the pulldown.

I certainly hope DB plans to add the ignorance algorithm to the new website soon.

Lee, good job explaining the u/ü issue at DB.

(Note to Lee that won't help jwm at all... So I went to bayern-fahrplan.de to sort out the "Fussen" stop. Looks like its short for Fussener Weg, a tiny street with 2 street addresses - 61 and 62 - which lies about 4 km outside the town center of Stephanskirchen, a town I've never heard of, and one that doesn't have a Stephanskirche at all! And the location isn't even a bus stop, just a location. But if you happen to live at Fussener Weg 61 or your car breaks down there, you can get an itinerary from there anyway, one that begins with a walk of 1.8 km to the nearest bus stop. Incredible, really, that a transport site can be this accommodating.)

I do not know when you are going. Right now the Dbahn website is routing you through Nürnberg for a 6+ hour train trip. It might be because they are still working on the Ansbach train station.

I really like Rothenburg ob her Tauber but I would wonder about the cost/benefit of taking that route now. If Rothenburg is not critical to the rest of the itinerary, I might consider an alternative like Nördlingen, another walled city.

Best to go from Fussen to Rothenburg by car on The Romantic Road. Augsburg is wonderful, also, several walled medieval towns.
https://www.romanticroadgermany.com

Best to go from Fussen to Rothenburg by car on The Romantic Road

I'm not so sure about that.

Far be it from me to discourage someone from doing the Romantic Road, but driving straight through is not the way to do it. It's just a winding, 2 lane road, choked in the summer with tour buses, trucks, and farm equipment. The thing that makes it special is visiting the towns along the way.

In 2007, I did the Romantic Road from Wieskirche (I'd already been to Füssen three times) to Würzburg in just over four days (by public transportation, BTW, not by car). I spent only an hour or so a day traveling and the rest of the time in the towns. I stopped in Schongau, Landsberg (overnight), Donauwörth, Harburg, Nördlingen (overnight), Dinkelsbühl, Feuchtwangen (overnight), Rothenburg (lunch only), Weikersheim (overnight), and Bad Mergentheim. I didn't spend any time in Rothenburg as I'd already been there twice.

Schongau was a disappointment, Landsberg was a pleasant surprise, Harburg was a pain getting to but if you're into castles, this one is really old, and intact. Nördlingen was my favorite stop, by far. It has an intact wall you can walk on. Dinkelsbühl was a disappointment, but maybe because it followed, and wasn't, Nördlingen. Feuchtwangen was not real historic, but pleasant. Weikersheim is not shown on the link in the above post, but was worth the stop, particularly the Schloßgarten. The Deutschordensmuseum (home of the Teutonic Knights) in Bad Mergentheim was worth the stop.

If you're just going to drive straight through, and not going to put in the time to actually stop in the towns, the road itself is not worth it.

I used Google Maps, put in Füssen to Rothenburg, and tweaked the route to follow the RR. Google Maps said the time, without stopping, was 5 hours, 3 minutes. The Bahn shows the time to go from Füssen to Rothenburg by train as 4 hours, 36 minutes, so you're not saving any time by driving it.