From London to Frankfurt - help me plan?

Don't miss visiting the Church of our Lady in Bruges to see Michelangelo's Madonna and Child. And definitely a canal cruise.
And you must reserve your tickets for Anne Frank online. Definitely check out the website in advance to know how their on sale dates work. It's basically the Tuesday at 10am (Amsterdam time) six weeks out, but a bit more nuanced. Highly suggest setting your alarm, don't wait until morning US time to get the tickets. They sell out quickly.

Welcome to this board with your first post. Have you been to Europe before? This is a lot of sitting on trains, checking in and out of hotels, and learning the transit and layout of many cities. Will any of you ever visit Europe again?

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

https://www.ricksteves.com/travel-tips

Don't overlook advance check-in, maybe 90 minutes, for Eurostar in either direction from the UK. Rules on their website.

It is certainly possible to spend a long time at Museum Ludwig, but what about Kolumba and Schnütgen? Don't overlook the Cathedral treasury. The excellent Applied Arts Museum has a lot of Renaissance and Art Nouveau, as well as Modern. Tilman Riemenschneider, anyone?

This will be our sixth fourth trip to London. We have been all over UK and France. We are not intimidated by public transit.

Edit to say thank you for the tips on tickets for Anne Frank. Very helpful!

Some destinations, like Anne Frank House, Rijksmuseum, and Van Gogh absolutely require advance, non-refundable booking. I think the Roman-Germanic museum in Cologne is currently closed for renovation. As is the Roman underground site, the Praetorium. But I haven't been there in some time.

I would point out that Cologne (and Aachen) are very well connected to Brussels by train. I personally find Antwerp a more attractive place to stay than Brussels. But the two unified art museums in Brussels are pretty important. As is the KMSKA in Antwerp.

It seems you have a lot of traveling between cities. Using trains as your main transportation I'm not sure how you fit anything else in.
Everyday you travel you lose at least four hours just on travel. One hour to pack, shower, eat and check out. One hour getting and waiting at the train station. Two hours for the trip between cities minimum. Then going to and checking into you new room could be an hour if your close to the station. So were close to five hours of travel. Depending on the time you arrive at the new city you may not even be able to check in. It may be too early. So what do you do with your luggage?
Now you get the afternoon to visit the sites you want to see which will also be the busiest time for tourists.
Now your worn out so you grab a bite to eat go back to the room and start all over again the next morning.
And you better hope there isn't a rail strike or delays on any of the legs.
Just my opinion why you need a minimum of two night stays if you are going to see stuff.

Good point. I’ve reworked the trip to have three overnights in Brussels, 3 overnights in Amsterdam, one overnight in Cologne, and then travel to Frankfurt late the last day. Will hire all private tours for cities and day trips. Will hire a car if needed. Thanks!

I think the Roman-Germanic museum in Cologne is currently closed for
renovation.

It is open, operating in a smaller, temporary location. IMO still worth a visit.

three overnights in Brussels, 3 overnights in Amsterdam, one overnight
in Cologne

In Amsterdam I suggest you add the Maritime Museum for this important aspect of Dutch history.

Regarding Cologne, the Wallraf-Richartz Museum has nice collection that extends from Gothic to the Impressionists. Ludwig is the modern art museum.

I would suggest staying in Bruges. It is the coolest city. Easy to walk and so much to see.
Here is something that you could do and still fit in two spots to see stuff.
Take the high speed train between London and Brussels. Get a locker for your luggage at the station, i used them last year when i made the same stop. The main Plaza and the Pis statue are near the station.
Here is what you could plan.
London to Brussels on the high speed train in the morning.
Get off at Brussels and look at stuff.
Then take the local train from Brussels to Bruges which is around an hour if I remember correctly. Now you arrive in Bruges in the late afternoon and you can check into you room, grab dinner and plan to see stuff the next day. This gives you two nights in Bruges which is really nice when most of the day tripping tourists have left for the day.
Now here is where you fit in a little nugget that you didn't have planned.
Take the train from Bruges to Antwerp which is a local train. Get off and visit Antwerp that afternoon. Going outside and looking at the classic Antwerp Train Station is worth the stop. It is one of the coolest stations in Europe.
Then take the high speed train between Antwerp and Amsterdam. Now you can check in grab some dinner and get a fresh start in the morning.
So now you get to see some stuff in Belgium and get to stay at a really cool city for two nights.

I would mention that if it matters, Amsterdam these days seems to be actually discouraging tourists. So there may be an unpleasant tone in the air.

That is something to consider about staying in Bruges. I don’t have any great desire to spend three nights in Brussels. Bruges and Ghent are more my style. I just don’t want to pack up my suitcase and move every day, although we could easily store luggage at train station. Appreciate the museum suggestions, as that is a big part of our vacations. I have read that Amsterdam is discouraging nuisance tourism. Who can blame them. We will do our best not to get drunk and throw up on their sidewalks, as we go to the Anne Frank House, the Riksjmuseum, and Van Gogh Museum. Perhaps we will find someplace nearby to make our home base like Haarlam.

I would like to suggest you add a night to Frankfurt and take the excellent Frankfurt on Foot walking tour. The city and its history will surprise you.

Yes, thank you for that suggestion. I was unclear but we will arrive late afternoon in Frankfurt and spend the night before flying out the next day. We love walking tours.

I agree with the above poster about really considering how long things take. I actually sit down and visualize what time we'd get up, finish breakfast, how much we're carrying, how to get to train etc. You sound like experienced travelers so I'm sure you will figure it out!

Your comment about trying not to throw up on the streets of Amsterdam made me laugh. After the highly successful Vermeer exhibit, I read an article about Amsterdam focusing on just the kind of tourist you are - museum lovers! And since you mentioned Ghent, here's an excellent blog about why it might be a good idea to spend at least a few nights there - https://michelledamiani.com/around-the-world/ignore-the-guidebooks-choose-ghent.
I've put Ghent into the 'Living Museum' category. Best to book ahead to see the Ghent Altar Piece. Sounds like a great trip!!

Thank you for the blog link. I’m going to read that now. I’m trying to decide if we will stay in Bruges or Ghent. Another person suggested storing luggage at the train station, see Brussels, and move on. I liked that idea a lot. We will get to Brussels early. I’m a vacation go-getter. We usually get at least 20 thousand steps a day. One backpack each. We are realistic about travel times, etc. Where am I from, we drive an hour to work and back daily in heavy traffic.