Germany (Rhine) itinerary advice

You're making a kind of zig-zag. Are you committed to flying into Berlin? How about flkying to Frankfurt, going directly to Rhine, then Heidlelberg, Rothenburg, Munich, Berlin.

"Longest train ride would be from Berlin into the Rhine area. I'd get in around 11am on the 21st. "

So you're leaving Berlin at 5:30 or 6 am?

"...the second would be a cruise up the Rhine."

Best to cruise the other way - downstream, with the current, faster. Bingen to St. Goar would include the best scenery in 1.5 hours. Or you can cruise to Boppard for a little more in 2.3 hours.

So you'd be smart to overnight in Boppard or St. Goar. On Day 2 you catch a train to Bingen and cruise back north - to the OTHER of the two towns for a visit. Both towns are charming and have stuff to do. St. Goar has Rheinfels Castle. Boppard has a cool chairlift ride, some wineries, and a nice old town.

Your train travel on Day 2 can be done on a Rheinland-Pfalz ticket day pass. It will give you a 20% cruise discount as well - just show it at the KD dock in Bingen.

About Day 1. Take the train from Berlin to Koblenz first that day. Stow bags in a station locker. Take a train 10 minutes to Braubach for a tour of Marksburg Castle. Then return by train to Koblenz and move on to your town of choice by train in the late afternoon.
Marksburg website

Her plan is almost a straight line, north to south, no zig zag at all. If you get out a map, you can plot the stops.

I do think it is too much to do in 10 days though, especially a city like Berlin. Two days only? Do you arrive on the 19th or on the 18th?

Much as I like Heidelberg, I would cut it from your list to allow more time in Berlin. You can do a cruise and visit 1-2 castles on the Rhine in one day. Are you arriving in Cologne, Koblenz, Mainz, Frankfurt airport, or Frankfurt city by train on the 21st? There is also little time to visit Munich if you are planning major activities and excursions all 3 days.

I would skip Heidelberg - out of the way, sort of interesting but not all that much. Just take a train to Würzburg instead. It's a Romantic Road town just north of Rothenburg and a good city to visit. You could stay there 2 nights and day trip to Rothenburg on 9/24. Or stay in 2 different towns if aren't averse to time spent packing and unpacking, checking in and out...

Main River Bridge in Würzburg
Residenz
Hofkirche at Residenz
Marienberg fortress

I agree with Jo that you can do a Rhine cruise and see a couple of castles in one day, that's exactly what I did last summer. I cruised from Bacharach to Boppard and then took train to St Goar and back to Bacharach.

I agree with Russ that you could skip Heidelberg and, as Jo suggested, add a day to Berlin. But I disagree about Rothenburg, doing it as a day trip is seeing the worst of Rothenburg - the crowds of other day trippers. Better to spend the night there and explore in the evening and morning and then move on. However, I must say that I did perfer Wurzburg to Rothenburg myself.

If you can't visit Rothenburg during the day because of the tourist horde, maybe it's not worth going to at all. There are good alternatives.

Iphofen is an old-world walled town that is easier to get to than Rothenburg (20 minutes by direct train vs. 1 hr.+ from train hub Würzburg) and is lovely at any time of day. Lots of wineries, artists, cafes, and very handsome old-world buildings and town walls. As in Rothenburg, Riemenschneider left works of his own there - The St. Vitus church of Iphofen has 2 Riemenschneider carvings. (Sorry, not much in the way of tourist trap shops or Schneeballen in Iphofen. It's an authentic town with a bit of class.)
Photos of Iphofen:

IPHOFEN

I would also drop Heidelberg in favor of more time in Berlin. Rick's Germany book suggests giving Berlin at least two full days (and three nights) but many people would appreciate a third day. While Rothenburg has the attraction of the more complete old town walls, Bacharach and other stops on the Rhine could give you your taste of smaller-town atmosphere and half-timbered architecture. Our tours do both, but they have the advantage of driving direct by bus, instead of taking trains with connections. Of course, packing light is a good train travel strategy.

If you choose the German Rail Pass with Twin discount, note that it also covers the direct (German operated) trains from Munich to Italy; the 11:30 a.m. daily direct train will take you as far as Venice for just a seat reservation. The pass no longer covers the K-D boats on the Rhine and Mosel, but gives you a 20% discount. Train tickets within Italy are relatively affordable for the typical tourist distances. Passes go on sale maximum 6 months in advance of travel and tickets and reservations maximum 3 months ahead.

I’ll arriving into Berlin on the 19th. Based off all the recommendation, I think I will cut Heidelberg from the list and spend additional time in Berlin.

I was going to take the train from Berlin to Koblenz and begin castle exploration. Sounds like I’ll be making Boppard or St.Goar my base along the Rhine.

I’ll actually be spending the night within Rothenburg. Found a place directly within the city itself. I figured most of the tourist crowd should be gone once the sun starts going down.

Outside of all the excursions I have planed for Munich, I should have at least a day and a half in Munich. There’s no way I can see myself sitting in a beer tent from Sunrise to Sunset.

Thanks everyone for the advice!