3 days in Feb Frankfurt to Dusseldorf

It is a poor comparison, because our target was a national plant show in Venlo, but we rented from the Cologne HBF and left Cologne immediately. We spent 10 days driving to Amsterdam.

I still fail to understand how anyone can need or want a car in Duesseldorf. Do you want to see Monschau?

Do they have the monthly "Fishmarket" festival in Ddorf in winter?

Our need for a car in Dusseldorf is due to a work related obligation. We're adding some vacation days into a work trip and looking for recommendations to make the most of it.

Since the old thread is lost, here are some (mostly summer-no boats in winter) Middle Rhine posts:

https://search.ricksteves.com/?button=&date_range=2y&filter=Travel+Forum&query=middle+rhine&utf8=%E2%9C%93

Although the Rhine Valley is the most obvious choice between Frankfurt and Dusseldorf, there are other opportunities for excellent sights west of the Rhone also, Cochem, Trier and Aachen for example.

https://www.cochem.de/tourismus/en/index
https://www.tourism.de/trier/
https://www.aachen-tourismus.de/en/

There is usually one ship per day going down the Rhine from Rüdesheim. Even sitting inside, it can be a pleasant ride unless it is foggy and then you would see nothing.

Have you considered spending a day or two in Frankfurt? Very historic and there are lots of interesting sites to see depending on your interest. Nearby is also Mainz, which is certainly worth a day sightseeing.

What kind of things are you interested in?

Thank you for the replies! We are quite flexible for our plans and are open to any suggestions. Actually Ms. Jo I was under the impression that Frankfurt was more of a business city without a lot for a tourist to do so I never really considered it but I think I was wrong. I will do some looking into it, thank you for the suggestion. We're up for almost anything - museums, local food, smaller towns, meeting local people, castle tours, etc.. Nick, Cochem was on my radar as well as Aachen! I have been to Aachen and would love to see the cathedral again and show my travel partner. As I mentioned, she hasn't traveled much, possibly never international, so I am hopeful she will have a positive experience (even though it'll be in February) and will want to see more in the future. We are meeting up with another person in Dusseldorf where we be working for a few days and then the 3 of us will head to the Netherlands for a long weekend.
Any more suggestions are welcome!

Frankfurt has a ton of museums, only Berlin has more. There are several medieval churches including one that was actually consecrated in 850, and the church that was the designated location for the election of the Holy Roman Emperors in 1356 for 400 years, later in the 1500's the coronations. Frankfurt was the center of Jewish culture in Germany for centuries and the site of the first enclosed Ghetto. Meyer Rothschild was born there and the Frank family go back to the 1500's here. There are great Farmers markets as well as the wonderful Klein Markt Halle and lovely residential turn of the century neighborhoods. Yes, we have skyscrapers and a lot of banks, but the city is so much more.

When in Feb? All the Fasching parades will be happening in many cities. Cologne is the larges, followed by Mainz, but the one in Frankfurt is pretty good one too, including on on the Tues. in Heddernheim called Klaa Paris. Smaller towns like Seligenstadt or Oberursel have nice little parades too.

"...how to best spend those 3 days..."

If your visit will include the Fasching (or Fastnacht or Fasnacht) celebration - especially Monday Feb. 24 (the day for Rose Monday parades, with very large street crowds) - you may have a couple of disincentives for booking in Mainz or Cologne...

low availability, high prices, and a sometimes-too-rowdy atmosphere when the usual inebriation reaches the wrong level.

If you want to visit Mainz and/or Cologne as they "normally" are, with all the sights and shops open to the public, I'd arrange that on another day.

OTHERWISE... I would suggest 3 nights in Mainz. Mainz is located where the Rhine and Main rivers meet, only 25 minutes by direct local train from FRA airport. It has a generous number of pedestrianized streets (pink on this map) that are great for car-free wandering around and sightseeing.

Lots of Mainz photos
Top 10 sights in Mainz
https://c1.staticflickr.com/9/8517/8466997951_748e0b61f0_b.jpg
http://www.neumainzer.de/wp-content/uploads/2015/06/Besuch-auf-dem-Mainzer-Wochenmarkt.jpg
https://www.tripadvisor.com/Travel-g187393-c218446/Mainz:Germany:Walk.Mainz.In.One.Day.html
https://www.mainz.de/medien/internet/downloads/MZ_Museen_englisch.pdf

From Mainz you can catch a northbound train for a day outing that takes you through the UNESCO World Heritage Middle Rhine Valley. The RE train will reach Bingen (gateway to the scenic part) in about 20 minutes. From there, it follows the river past many castles and craggy cliffs (with a very rugged appearance in winter) and through the old-world towns of Bacharach, Oberwesel, St. Goar, and Boppard. These will all be VERY quiet at this time of year, but getting off in one or more of these attractive places can still be rewarding. The half-timbered buildings in Bacharach will still be impressive, and if the weather is OK for an extended walk, Oberwesel's old-town wall is there to explore. I would make a full day of it - continue north to Koblenz and switch trains there for a return along the east bank for a different perspective of the river gorge. Braubach (10 minutes from Koblenz) is home to Marksburg Castle (never-destroyed medieval castle, open all year.) Rüdesheim (further south, across the river from Bingen) could be a good stop in the p.m. Then return by train to Mainz.

Map of the Upper Middle Rhine Valley train lines

If you wish to visit Frankfurt, you could do that either as a day trip from Mainz, or upon arrival (stow bags in a Frankfurt station locker, sightsee, then catch the train to Mainz later.)

When you travel to Düsseldorf, you may want to make a stop in Cologne on the way - see the Dom (cathedral) and a museum or two. Stow bags using Cologne station's luggage storage system.

There is nothing wrong with Frankfurt; I've been there twice, for multiple days both times. But the smaller and older towns and cities around it are more of an attraction for me. (Link at end has some notes, but it may be too dense for your limited time. Page down to "Fachwerkstraße".) When my wife and I were younger, we never rented a car, but stayed in large cities (by train) and did an occasional daytrip by train. But I feel that many of the sights around Frankfurt are too small to justify a RADIAL train trip that (because the rails are radial) excludes the chance to go elsewhere the same day - that's why we were glad to have a car, and to stay in a suburb (Kronberg.)

I am not suggesting that there is anything incorrect about Ms. Jo's reports. But as a native of NYC, I simply have an alternative opinion about some of the major cities of the world. You have to decide what things you want to do, preferably before your trip begins.

https://community.ricksteves.com/travel-forum/trip-reports/baltic-germany-fachwerke-landesgartenschau