FRA, Cologne Cathedral, and Rhine Valley

Pick-up rental car when you leave Cologne.

FRA to Cologne by train: https://int.bahn.de/en

Check requirements for driving permission (not license only):
https://bmdv.bund.de/SharedDocs/EN/Articles/StV/Roadtraffic/validity-foreign-driving-licences-in-germany.html

Assuming you mean Sankt Goar? You have to watch the spelling because there are a lot of close named towns (I know 5 Neustadt's) and a single letter can get you somewhere other than where you want to be. (Regensberg is over 100 km from Regensburg.)

It's a minimum 2 hours drive to Koln from FRA, and then you have to deal with parking, which can get expensive if you get it wrong. Tickets are a thing in Germany. The train takes 55 minutes. Put your stuff in a locker at the FRA station and take the train, round trip. Then when you come back get you gear and take the train to St Goar, because it's a very small town and they don't need another car to park.

Or even better, once you get settled at St Goar take the train up to Koln.

Frankfurt airport does not have any lockers (only a storage facility) and if their end destination is St. Goar, it makes no sense to come all the way back to the airport just to get luggage and then back track to St. Goar. Just take your luggage with you and store in the train station at Cologne while you visit the cathedral, then pick it up and head to St. Goar.

Honestly, though, this sounds like an awful lot to do on your arrival day. Where are you flying in from? Can you take the train straight to St. Goar and visit the Cologne cathedral the next day? Maybe get your car then and drive it back to St. Goar?

Where is best place to pick up our rental car..FRA upon arrival,
Cologne, or even FRA after Cologne? We will have our luggage too.
Thanks

The devil's definitely in the day-1 details. Driving after a long overnight flight across many time zones is somewhat risky, especially for the long drives you are proposing - which makes Jo's question about where you fly in from a very reasonable one.

That said, even after just a 1-hour flight, I would NOT recommend the 4 hours of driving you have in mind for FRA > Cologne > St Goar. The slickest way to get Day 1 underway is to catch a morning train (maybe the 9:10, non-stop to Cologne!) to Cologne's main station, Köln Hbf (arrives 10:05.) The Cologne Cathedral is right next door to this station.

"Luggage" - Everyone brings it. But the wise traveler follows Rick Steves' packing advice and follows it religiously:
https://www.ricksteves.com/travel-tips/packing-light/packing-smart

Luggage storage - Then main station in Cologne has an automated bag storage system. This guide to the station has some details.

However... it would surely be my choice to book Night #1 in Cologne. After arrival there, I'd drop bags at the front desk of my hotel near the station. I'd spend a couple of hours at the cathedral, get lunch, then check in and tend to my personal needs. After that, I'd look into something else in Cologne, a walkable city with many good options.

If you are convinced that Night #1 must be in St Goar, then you can catch a DIRECT train there on Day 1 (14:56 - 16:55, for example.) Otherwise, you could get a car the next morning and drive there, well-rested.

Do you need the car for St Goar? I don't know. Most people don't. Some outings might call for one. What outings do you have in mind? It does not help with a river cruise. Trains connect all the riverfront towns. It may be best to pick up a car in nearby Mainz, Koblenz or Wiesbaden once you are ready to leave the area.

(On your TA forum thread, where you mention Bacharach in place of St Goar: the train ride from Cologne I suggested will take just 10 minutes more if Bacharach is your goal. Also, prior to finalizing your plans, please give careful consideration to the cautionary comments made by A Mainzer and detbo about driving.)

Although Cologne is a favorite of mine, and there is lots to see besides the Cathedral, it is a very "urban" city. By that, I mean that is quite risky to leave luggage that even remotely suggests its presence, in a parked car. I don't know if Ms. Jo meant that you should carry the luggage from a giant pay garage, to the train station storage, or if she was assuming that you would rent the car in Cologne. (That would be because the train makes so much more sense for your trip as far as St. Goar.) That is, Cologne is an exceptionally WALKABLE city, and the Cathedral is only steps from the HBF.

Neither the train nor the car route along the Rhine is remotely as scenic as the boat rides. But because the boats aren't frequent enough to be "Hop On, Hop Off", a car might be helpful for planned multiple stops in one day.

I rented a car at a hotel at the edge of Cologne, the Netherlands side, because that was our direction of travel. I didn't want to drive inside Cologne. Of course, you need a city bus to get your luggage near such a rental. Last time I rented at FRA, they didn't have any automatic transmissions except a giant Transit van, which they offered to me at the sedan price. When I asked for a regular car with standard transmission, we had to wait almost an hour for one to be turned-around and made available to us. (Big-three rental.) As normal in Europe, check exact hours and meal breaks for any non-airport car rental office.

I meant for them to take the train to Cologne, store their luggage in the lockers at the station, visit the cathedral and train to St. Goar. I don't think they should drive a car at all that first day.

Thank you, everyone. We are arriving FRA from US on a Friday morning, staying in St Goar for two nights, and then driving to Rothenburg ob der Tauber on Sunday. I know it’s a very short time and the only way I could see squeezing in the cathedral was on Friday, but I definitely question whether it’s doable or worth it. Only interested in the cathedral ..one of my favorite topics in college art history. We could also go to Ulm cathedral instead but i’m sure it’s not the same. Reality check from you all is fine!

You are being told that your time wasted in travel, paperwork, and parking search on these days will be less if you use the train. You may not believe it, and you have to make your own decision. Cologne is, literally, famous for how walkable from the HBF it is for tourists, even if they want to see more than the Cathedral.

https://community.ricksteves.com/travel-forum/germany/can-i-see-enough-of-cologne

I have not been to Ulm. Are you flying home after Rothenberg?

From your responses, I am leaning toward taking a train from FRA to Cologne, storing our bags and picking up rental car at the train station. Then our bags are secure and we can walk Cologne. Are rental lockers big enough for carry on size suitcases? Still not sure it’s worth the effort but will need to decide since that determines rental car pick up.
And no, we aren’t going home after Rothenburg..traveling on to meet up with friends in Munich. Dropping car there. Thanks

Are rental lockers big enough for carry on size suitcases?

Please see my previous post about the automated system and the link I provided to "Man in Seat 61" website.

In the last 25 years, 11 trips, I've spent over 150 nights in Germany, so over 160 days. 80% of my nights have been spent in towns under 20,000 Pop., so I've not restricted my time to large cities, I've spent most of my time in small towns. I've never needed to rent a car. German Rail is a huge rail network, and it's augmented by an even bigger bus network. For trains, I rarely use long distance trains; only for long trips. Then I usually buy heavily discounted, advance purchase Spar-preis (Savings Fare) tickets. Between advance purchase tickets, regional passes, and local tickets, I'm pretty good at minimizing rail travel costs.

For most of my recent travel, I've compared the cost of a car rental with my actual rail ticket expense, and renting a car usually would have been two to three times as expensive.

Your problem with using the train to Köln the day of arrival is that you shouldn't use a discounted ticket because it is train (time) specific, and if your trans-Atlantic flight is late, which they often are, you could lose your ticket and have to buy a full-priced one. A fully flexible, long distance (ICE) ticket from the airport to Köln is about €100/P. If you purchase a Deutschland Ticket, valid on regional trains, it's €58/P and is valid for one calendar month. It would cover your travel by regional train from the airport to Köln to St Goar to Rothenburg to Munich. From the airport to Köln by long distance trains takes about an hour. By regional train it takes from 3 to 3½ hours. It takes almost 2 hour to drive plus the time to pick up the car.

Probably the biggest problem with using all rail is that the trip by car to Rothenburg is about 3 hours plus stops versus about 6 hours by rail with 3 or 4 changes.

As others have suggested, take the train from airport to Cologne. Everything you'll want to do on a day trip to Cologne will be in walking distance from the train station (cathedral, chocolate museum, old town). I'd recommed Brauerei zur Malzmühle for a meal. Can't go wrong sampling all the kolsch either.

I did a similar trip last summer where we trained to Dusseldorf (day trip from there by train to Cologne), then rented a car to get to Rhineland (Rudesheim), then drove to Rothenberg, then eventually to Munich. The drive to Rothenberg is easy and pleasant.

Thanks to everyone for their feedback!

And, if you can't get Koln into the time you have, you could always just go to Mainz and see the Chagall window there.

I will definitely look into the Chagall window. Thanks for the suggestion.