Hello. We will be in Nuremberg at the end of a Viking cruise in July and plan on doing a day trip down to Rothenburg on a Saturday. Do we need to plan and buy the train tickets in advance or is it ok to buy them the day of the trip? I don't know if the early trains may sell out. Thank you in advance for your replies.
The trains do not sell out, so buy it when you get there.
Buy an "VGN Tagesticket Plus" for €19.70 from any DB or VGN vending machine in the station (much cheaper than two regular tickets). It's a day pass - in your case: a weekend pass - valid in the entire (large) VGN area. You can take any local train (EXCLUDING connections that involve an IC from Nürnberg to Ansbach, but there are only very few of them anyway) and you can do side tours at will.
Don't buy anything from home for this trip.
From a ticket machine at Nuremberg's main station, buy a "VGN Tagesticket PLus" - a day pass good for trains, buses, subways in the region. (Use regional trains - not the high-speed trains.) It's €19.70/day for two adults and covers as many trips as you like on the entire regional network, including Rothenburg:
https://www.vgn.de/en/tickets/all-day-ticket-plus/
https://www.vgn.de/media/schienennetz-gesamtraum-vgn.pdf
To find regional train SCHEDULES to R'burg and back, consult the DB Railways page - it will show you changes of train and other details. Be sure to click on "only local transport" in order to pull up trains that are eligible for the VGN day pass:
https://www.vgn.de/media/schienennetz-gesamtraum-vgn.pdf
The VGN day pass can be bought from a bus driver or at a subway station in Nuremberg as well - good to know in case you require bus or subway transport to the train station in the first place.
Thank you very much for your replies. We will try and buy the pass.
When you get the pass ticket out of the machine write the name of the primary traveler in the place indicated on the front.
We did this exact thing and it is super easy! We did the VGN Tagesticket like others have said-the machines are easy to use. There was a lot of room on the train. Have fun-we loved Rothenburg! Stay for the Nightwatchman tour if you can. I think it is at 8 pm...it is a hoot.