I am going to Germany early July, with focus on Berlin and Munich. However, to fly to Berlin is about $700 more with a minimum 6.5 hr layover vs flying direct Frankfurt (4 hr train to Berlin). Can fly home direct Munich. Currently I'm thinking land in Frankfurt and head to Koblenz for overnight. Do focused Rhine boat tour (between Bacharach and St Goar) day one (6/30). In morning see Burg Eltz and then head to Frankfurt. Self guide walking tour Frankfurt before train to Berlin. Berlin 7/1 (late)- 7/5 then Munich 7/5-9. Day trip from Munich to Neuschwanstein & Linderhof . I orginally debated overnight Fussen to do spa but logistically seems impractical. Does it seem worthwhile to do Koblenz/ Rhine? I thought it would be nice to see some castles and scenery before hitting the cities? Worth it to do Burg Eltz vs something closer such as Marksburg? I realize Koblenz is a bit lacking, but makes sense for the trains, especially as it appears while I'm there, many previously trips are not as many train lines under construction (when I first looked, train Berlin to munich 4 hrs or under in spring, now almost 6.....) Thanks
Don’t just take the boat between Bacharach and St. Goar !! Take it from Bingen or Rudesheim to St. Goar or Boppard. Rick Steves’ recommendation to limit to St. Goar/Bacharach is based on his need to cram as much as possible into his tours, not the best for an independent traveler. I have taken the boat several times, including from Mainz to Cologne years ago when that was an option. Last time I needed to go from Rudesheim to Bacharach and rather than taking the ferry across to Bingen and then the train ( as I had to get to Rudesheim), I went by boat. That short section is very scenic.
I would catch the train straight from FRA to Bingen Rhein Stadt and board there for the cruise. Do it just as Stephen suggests but get off the boat in St Goarshausen (across the river from St Goar) so that you can take the 20-minute train ride directly to Braubach (home of Marksburg Castle.)
Some B&B's there right in town (used often by hikers on the Rheinsteig trail.)
Privatunterkunft Metz, Karlstraße 11
Goldenen Schlüssel (w/restaurant, great food)
Other options online. For these just send an email inquiry.
Braubach is gorgeous: https://www.stadtbild-deutschland.org/forum/index.php?thread/7322-braubach-am-rhein-und-marksburg-galerie/
In the morning: Tour Marksburg if you didn't on Day 1. Braubach is on a direct train line to FRANKFURT central station.
Burg Eltz would be much more time consuming.
If you are following the Rick Steves walk in Frankfurt, you will miss half of the most interesting sights to see here. Add in the Jewish Holocaust Remembrance Wall, the Karmeliter Cloister, Alte Nikolai, and St. Leonards, as well as the new Alt Stadt with Franconoford.
Events in Frankfurt and along the Rhein in early July:
Opern Platz Fest, Frankfurt Alte Oper – 25.06-4.07
Sekt & Biedermeier Fest, Eltville – 4-7.07
Höchst Schloss Fest, Frankfurt Höchst – 5-14.07
Rhein in Flames, Rüdesheim – 5.07
If you can get a room in Rüdesheim for the Rhein in Flames, this would be preferable to Koblenz. I am sure they are booked up by now. Perhaps Bingen?
I don't think you'll have enough time to do Burg Eltz and then wander Frankfurt before getting on a train. The castle doesn't open until 0930 and there will be a line of tourists waiting for that to happen. especially in late June/early July. Plan on getting back on the road around noon. But the drive is also slow to Frankfurt due to construction, and Monday (30 June) is the worst day for truck traffic. It can take at least an two hours for that drive when traffic is good.
Koblenz is really a good town to visit, and I greatly prefer Festung Ehrenbreitstein to either Marksburg or Burg Eltz. If you have any interest in military history I highly recommend the Wehrtechnische Studiensammlung in Koblenz as one of the best, often overlooked, technical museums in Europe.
Koblenz is a mostly-modern city that was crushed in the war and rebuilt ala 1950's; it does have a smallish old-town zone, and Ehrenbreitstein Fortress, on a hillside across the river from Koblenz, is one of the town's main draws. However, in your post you mentioned Eltz and Marksburg - two 12th-century castles - and the river cruise - as your main objectives. If you are making your quick detour to the Middle Rhine valley with medieval structures like these in mind, as most visitors do, then I am guessing that Koblenz and Ehrenbreitstein, an 18th-century military installation, might be somewhat lower on your list of priorities, something you might include if you end up with more time after your cruise and castle tour.