Rhine Valley Day trip from Frankfurt

If you mean Upper Mid Rhine Valley:
Use public transport RMV to travel to Mainz or Bingen (South bank) or to Eltville or Rüdesnheim (North bank). From there you can start biking or ferry cruising, e. g. with KD or another river cruise line. Check their schedules to get an idea what you can see in a day.

there is an almost identical thread, last updated yesterday, it may answer your questions, but does not address the idea of bicycling (I'd worry that you wouldn't have enough time unless you are an especially fast cyclist) - have a look at https://community.ricksteves.com/travel-forum/germany/day-trip-fron-frankfurt-airport-to-rhine-river-car-recommendations

There are a lot of places to see like Mainz, Burg, Bacharach etc....
What can I see in one day.

Biking will indeed be time consuming. So will cruising. You will see more by sticking with the trains, the quickest way to move from place to place. If your goal is to see some small, old-world towns, some castles and some nice scenery, the trains will take do that. The river scenery from the train windows is wonderful, so be sure to sit on the RIGHT side of the train for the best views. You will get in lots of steps on this day... wear comfortable shoes. Get an early start and make BACHARACH your first destination. There's a DIRECT regional express train from Frankfurt (6:59 - 8:03) which will allow you some time to explore the half-timbered buildings there.

From Bacharach, continue north along the west bank of the Rhine on the same train line. Oberwesel (5 min. away,) St. Goar (another 5 min.,) and Boppard (another 10 minutes) are possible destinations for stopovers. Focus on the line just south of Koblenz:

https://www.duesseldorf-blog.de/wp-content/uploads/2008/12/karte.gif

Continue your train hopping to Koblenz (15 train minutes from Boppard,) a rail hub where you can change trains for a southbound excursion along the east side of the Rhine. Braubach and Rüdesheim are probably the two most productive stopover options on this side:

https://rheingaulinie.de/files/rheingaulinie/files/Fahrplan/fahrplan.png

(The actual train time for Koblenz > Braubach > Rüdesheim is one hour, not including stopover time.)

Rüdesheim marks the southern end of the scenic Rhine Gorge section. It's a nice town that in the warmer months will still be active in the evenings. From Rüdesheim it will take 70 minues for the return train to Frankfurt, with trains running late into the evening.

You will not have time for ALL the towns I've suggested stopping in. Do some research on the suggested stopover towns to see what interests you most. St Goar has Rheinfels Castle Ruins. Boppard has a great chairlift ride with a superb view of the river valley. Braubach has Marksburg Castle. Also research the train schedules and put together your own working itinerary, based on your priorities. You can change it as you go, but it's good to have a plan:

https://int.bahn.de/en/

I have deliberately left out Mainz and Koblenz for stopovers, not because they are worthless, but because they are larger places that don't have much to do with the old-world Rhine vibe most people want, and because of the time they would require. You mentioned "BURG"... which means "castle" but is not the name of any town on the Rhine.

If you do want to bike, you can easily rent in Bingen, and to save time put the bike on a train and return from any of the towns on that side of the river. Trains run every 30 minutes.

I want to piggyback on this thread to ask some questions about this day trip. We're a family (cpl + 11yo) travelling through Frankfurt. We will be in Frankfurt for 3 nights. We want to do a 1 day Rhine Valley train trip.

Currently, we are on vacation in our home country so pretty much travel fatigued, so dont want to do a lot of walking. We want to soak in the nature, and enjoy the general vibe of the place. Till where should we travel, I am thinking Boppard. What is a good point to do the cross-river boat?

We're thinking of stopping at these stations:
Bacharach: Altes Haus, St. Peter’s Church
Oberwesel: Schönburg Castle OR Sankt Goar: Rheinfels Castle: which one is more convenient?
Boppard: Altstadt, Rheinallee, Römer-Kastell, Severuskirche

Please help.

Well, you may see some sun on Friday. Rain tomorrow.

The only ferry I've used is the one at Bingen, which isn't going to help much. Plus a lot of the small town amenities are still closed for the season. If you're in Frankfurt this weekend, you're going to have all the Fashing events between there and Mainz from now until Tuesday.

Three towns will be a lot of walking.

I suggest Bacharach + Boppard. In Oberwesel, you cannot tour Auf Schoenburg. It's a hotel. In Boppard you might also enjoy the chairlift ride and the excellent view of the river valley from the Gedeonseck outdoor terrace restaurant.

Rheinfels Castle is not in Oberwesel but in St Goar, right in between Boppard and Bacharach. There is a bus connection from town that will get you up to this set of castle ruins; you can board at one of the stops in town, or ride the bus to Rheinfels directly from Bacharach:

https://www.vrminfo.de/fileadmin/data_vrminfo/News/2024/Fahrpl%C3%A4ne_OMT/681_2024-08-01.pdfr

The St Goar ferry crossing is the handiest one to use. Once on the opposite riverbank, walk to the St Goarshausen station and ride the train back to Frankfurt from there. The train stops in Rüdesheim, not a bad town to visit or have dinner in.

Yep, the big Fasching Parade is in Frankfurt on Sunday and in Mainz on Monday. Another one is on Tuesday in Heddernheim, if you are still here.
Visiting Burg Rheinfels in St. Goar is my recommendation. See if you can get on one of the tunnel tours. Even if it is in German, your son will enjoy it as it is unique. Heck, I enjoy the tunnels and I am a senior!

Do as KGC recommends and rent a bike in Bingen. It’s only 45 km to Boppard which is not far if you are a decent cyclist. I used to ride 30 miles before breakfast.

I would stop in Bacharach. Walk the Malerwinkel. If you want to see a nice castle ruin where you will probably be the only visitor, take the short detour to the suburb of Steeg and walk up to Burg Stahlburg.

On to Oberwesel. See the big red church near the train station - Liebfrauenkirche - my favorite church in Germany. Walk a portion of the town wall

In Boppard, take the chairlift. The view coming down is my favorite view of the Rhine.

Train back to start

pvcaad: Please tell us WHEN you will be in Frankfurt. Some of us are making suggestions that may not fit your time frame at all.

Also... Like Rheinfels in St Goar, Burg Stahlburg is a set of ruins. Depending on what you are hoping to see, you may want to focus on the other riverbank instead. Marksburg Castle (open year-round) is the one medieval Rhine castle which survived intact across the centuries and can be toured:

https://www.marksburg.de/en/circuit/#/

Braubach, the home of Marksburg Castle, is a small but very attractive old-world town about 12 train minutes south of Koblenz, on the same side of the river as Rüdesheim and Eltville, two other worthwhile towns. And all these towns have direct trains from/to Frankfurt:

Rail Map: https://rheingaulinie.de/files/rheingaulinie/files/Fahrplan/fahrplan.png

3 pages of Braubach photos:
https://www.stadtbild-deutschland.org/forum/index.php?thread/7322-braubach-am-rhein-und-marksburg-galerie/

We're thinking of stopping at these stations:
Bacharach: Altes Haus, St. Peter’s Church
Oberwesel: Schönburg Castle OR Sankt Goar: Rheinfels Castle: which one is more convenient?
Boppard: Altstadt, Rheinallee, Römer-Kastell, Severuskirche

Having visited Bacharach, Oberwesel, and Sankt Goar last summer, I would choose Sankt Goar over Oberwesel. Nothing against Oberwesel, but Bacharach gives you a very similar vibe.

We did the wine wheel at Altes haus, which was a lot of wine. Be prepared to share or go with a smaller sample.

Oops - it’s Burg StahlbERg. Anyway, it’s the ruin obove Steeg. The youth hostel castle above Bacharach is Burg StahlECK. These two are sometimes confused in listings

Thanks for all the suggestions, I will go through in detail.
We're reaching on Mar 6th at 7 am. Will explore Frankfurt.
Mar 7th will be our Rhine valley train trip. I dont mind this to be a long day, we will rest next day or do some light activities nearby.
Mar 9th noon is our flight.

With those dates, Fasching/Fasnacht in Mainz and Frankurt is over with; the day cruises and the Boppard chairlift are still dormant for the winter (as are towns like Bacharach, Oberwesel, St Goar and Boppard, all within the Rhine Gorge.)

A visit to Mainz (which is outside the scenic Rhine Gorge) will require most of a day. You may be able to fit in a train ride to Bacharach/Oberwesel and back as well, but don't count on more than an hour or two in one town or the other.

Alternatively, you could sightsee in the Rhine Gorge by train along one riverbank to Koblenz, then return to Frankfurt from there along the opposite riverbank; with this option I'd recommend stops in Braubach (hike or taxi to Marksburg Castle for the tour) plus some time in Rüdesheim, which will be a little less sleepy than the other Rhine towns. A stop in Bacharach or Oberwesel might be possible as well on this loop - check the DB schedules to see.