Train between Cologne and Frankfurt along the Rhine Valley

but would it be traveling too fast to appreciate those views of the castles?

The ICE cannot travel any faster than an RE because of the winding route. The difference in travel time is only due to the fact that it only has two stops (Koblenz and Mainz)

BTW. please note that some ICEs depart from Köln-Deutz (one S-Bahn stop from Köln Hbf)

There are no RC trains.

ICE, IC, and EC trains are "long-distance" trains. All of these use the Rhine's west bank.

There are two types of regional trains that serve the same riverbank: RB (Regionalbahn, the most stops)
RE (Regional Express, fewer stops)

The long-distance trains generally make the fewest stops. However, from the main (Hbf) Cologne station, the station that is closest to most things in Cologne, you will still need to transfer to Cologne's Messe-Deutz station (across the river from most of Cologne) by regional train or S-Bahn before boarding these trains. See map.

The really short trips (like 1 -1.5 hours) you will find at DB from Köln Hbf to Frankfurt Hbf all bypass the Rhine Valley.

It sounds like you do not wish to make any transfers, but that's not possible unless you are actually starting from Messe-Deutz and using the long-distance trains.

"...would it be traveling too fast to appreciate those views of the castles?"

You can catch glimpses from all the trains - you'll look out across the river to the ones on the opposite river bank. The ones on the same side of the river as your train will not be visible since they are high on the cliffs above your train. All the trains go too fast for real "appreciation."

I suggest that you arrange to get off the train in 1 or 2 places for better viewing. Any of the regional-trains-only tickets will allow you to hop off and hop back on a later train after an hour or so. With these tickets, a change in Koblenz is required. I'd break the journey into a two-part train itinerary as follows from the DB site. Before searching, be sure to click the "only local transport" option to get just the regional train options:

1) Köln Hbf > St Goar: (a change of train at Koblenz Hbf will appear.) Through this part of the river, this west-bank perspective offers the best views.

2) St Goarshausen > Frankfurt Hbf (this train ride uses the EAST bank.)

St. Goar is quite small but stopping there provides one of the nicest views on the river. The walk from station to the riverfront and the ferry is very short. Also, there's a FERRY CROSSING there. Use it to reach St. Goarshausen on the other side and enjoy the views on the way. Then ride the "VIA" train (a regional train) south along the east bank from there to Frankfurt - the views from that side across the river are very good.

Here is the St. Goar > St. Goarshausen ferry schedule. 2-3 crossings per hour. €2 to cross.

The Day Ticket for Germany will allow you to use any regional trains you like... all day long on Sat or Sun, after 9 am on weekdays:
https://int.bahn.de/en/offers/regional/day-ticket-germany

My opinion is that the view from the dayboats on the river is far superior. And it is not necessary to ride the boat its full route. We used the KD boat from Bingen to Boppard, and saw "everything." You may find the local train useful for getting back to your hotel or car. Many rail stations are unattended, with only machines for tickets. The boat can also provide a modest lunch, with no loss to touring time.

Tim is right about the views from the cruise boats, of course. Boat schedules are not yet available but cruises normally begin during Easter week.

If your trip is at least that far off, a cruise could be part of your Cologne > Frankfurt train trip, which will take most of a day:

• Trains to Boppard or St. Goar

• Boppard or St. Goar > Rüdesheim cruise with KD
  (2023 data: €36 and 4.25 hrs from Boppard, or €25 and 3 hours from St. Goar. The walk with bags is easier in St. Goar.)

• Direct VIA train from Rüdesheim > Frankfurt

Thanks for asking this question, Josh, and thanks for these very informative answers, Russ and Tim and Augsburg. Bookmarking this thread for reference when I am ready to do some part of this trip !

@Kim: Since you may "do only part of this trip," I suggest you re-post before you do. No two trips to this area are the same, so yours will likely require a different strategy.

Thank you everybody for your help.

I would have totally missed the part about how the fastest ICE trains were starting from Messe/Deutz and not the main station in Cologne.

Since I'm traveling with luggage and an elderly person in my travel party, I was hoping avoid transfers but that doesn't seem possible.

I think if you check the DB site, there are direct, ICE trains from the main station in Cologne going to the Frankfurt main station. They take a bit over an hour.

@Jo: The OP is aware of the direct high-speed trains to Frankfurt but is attempting to route his journey via Koblenz and the Middle Rhine Valley instead.

Agreeing about the boat views being preferred. Generally, the trains run along the bottom of the hills, near the river. The castles are up on the hilltops. So you have to crane your neck pretty good to look up and see anything, especially depending on the sun's angle.

Josh, I can understand that switching to the boat for a small part of the trip is too much for your group. But it's a wonderful boat ride. I just want to make sure you know that the "city view boat trip" from Cologne is barely worth the time. It does not cover ANY of the historic and scenic part of the Rhine. Cologne is a wonderful and "walkable" visit, but it is not useful for the "Middle Rhine" scenery. If your older guest is mobile without luggage, it's entirely practical to take a train outing to Bingen, even though it's "back-tracking". It depends on what your overall priorities are.

I'm not an expert about this, but note that there is a train line on each side of the river.

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

The ICE runs on an entirely new-build route between Cologne and Frankfurt (as far as I know, the highest-speed line in Germany) and does not run along the Rhine Valley at all. It is possible to get a single RE train all the way from Cologne to Mainz along the scenic Rhein valley route and then change there for Frankfurt.

@Philip:

"The ICE runs on an entirely new-build route between Cologne and Frankfurt (as far as I know, the highest-speed line in Germany) and does not run along the Rhine Valley at all."

• There are in fact IC and ICE trains that travel through the Rhine Valley in addition to the ones on the high-speed railway you refer to... 7 of them tomorrow morning between 6:00 and 12:00. Travel time is just under 2 hours.

"It is possible to get a single RE train all the way from Cologne to Mainz along the scenic Rhein valley route."

• You are correct that some trains do that... but it's not the RE train. With the RB train, you can stay on the train through Koblenz and on to Mainz. I assumed the RE train from Cologne when I referred to the "required" change in Koblenz (which in fact does NOT travel all the way from Cologne to Mainz.)

• The RE train sequence to Frankfurt (with required change in Koblenz) takes about 3.25 hours with no stopover time.

• The RB > change in Mainz > Frankfurt sequence you suggest works also but requires roughly 30 minutes longer to cover the same scenery. So the RE sequence makes more sense to me if the OP is not planning a stopover anywhere and wants only the train ride and the views from the west bank.

If the OP opts for a stopover in St. Goar (as I suggested) for a longer look around... then the RB train from Cologne you mention DOES make for a faster way to reach St. Goar - with no changes of train.

After that, the OP has two routing options to reach Frankfurt...

• regional train sequence with one change of train to Frankfurt along the same river bank (trip length = 1.5 - 2 hours)

• ferry crossing to St. Goarshausen + DIRECT regional VIA train to Frankfurt. This train takes 1 hr., 37 mins.

I suggested the second option even though it will require a little more time to ferry over and walk to the station. The views of this part of the river from that side IMHO will be better. And the entire train ride will be direct.

I can't say whether or not the OP will choose to get off in St. Goar at all, or to incorporate a river cruise, or to use the ferry crossing as suggested. But the OP will have to get off one train and onto another at least once, somewhere. Traveling "with luggage" and "with an elderly person" introduces variables that defy recommendations from strangers like us.

St. Goar itself is very compact. The station, the market square (cafes/restaurants) and the boat docks are all within a few steps of each other. St. Goar map:

https://www.rheingucken.de/goar/stadtplan-st-goar.html