budingen

Yes, you go to the main train station, the Hauptbahnhof. You can either use the DB website or the RMV website. I prefer the latter, as these trains fall under the RMV/local transportation prices as well as the Deutsche Bahn. Switch the website into English. A group day ticket will cost 25.70 and will be valid for up to 5 people.
www.rmv.de These are Regional trains, and you will take the train to Gelnhausen, then switch to the train to Büdingen. There is about a 13 min. time between trains, so plenty of time. Once you get to Buedingen, walk down the street next to the train station, about 15 min. until you get to the city walls and the Jerusalem Gate. I recommend making a reservation with the toursist info there for a private tour in English. They only charge 41 euro for a 90 min. tour, but this tour takes you inside of the city walls, and up on the Hexen Turm. They are really cool inside, and the only way to see them is on the tour. Make sure you write down the times for the return trains, as they stop running at 19:30 and there is only one train an hour from Buedingen to Gelnhausen.

Thanks - this is a big big help. I saw on the DE site 3 stops for Budingen (bahnhopf, and what I think was east and west). Knowing the trains stop is also helpful. Sadly tho, its just me as solo ....no group discounts.
Any restaurant tips?

Those other stops are in case you want to take a bus from the train station to other areas in Büdingen. There is only 1 train stop in Buedingen. The ride is about 15 min. from Gelnhausen. A single, one way ticket will be 7.30 euro. I would still go ahead and reserve a tour for yourself. You will be so glad that you did. The 41 euro for this tour is well worth it. Once you go inside these massive walls built in the 1300's, you will see what I mean.

And once you return, please help spread the word... that there are, in fact, other preserved walled towns in Germany besides Rothenburg that are worth visiting.

Just got back, delightful town, full of surprises around every corner. Getting there mid-day by public transport not a dream but doable (sbahn to regional to bus, no trains mid-day). And with trains running late 50% of the time for me this summer, no surprise I missed first bus. But still worth it. Anyone who organizes photo clubs or teaches photography should schedule a trip there. That should spread the word.
It is beautiful and I don't think I could have bought a tshirt or ornament there if I tried. Not sure you want to spread the word...Jo, I didn't do the English tour. I am a law student and that is not a student budget price. Sounds great though.

Glad to hear you liked Buedingen cj. I always enjoy going there and though I have a pretty good collection of photos of the place, I always take more. The Christmas market there is a treat, though only held one weekend in Dec. and when they have their medieval market in the summer, it is truly a step back in time.