I want to take a Rhine cruise from Koblenz and plan on getting a ticket where I can get on and off as I go. I have two things I need though. I want to go to Bingen to visit the museum. I also want to stay overnight in a castle. I can't find a castle that's a hotel in Bingen. I've never been to that part of Germany so don't know the best way to go about planning.
"I can't find a castle that's a hotel in Bingen." There aren't any, that's why. There's only one castle in Bingen that isn't a ruin, and the town government uses it for office space.
You might do better by taking the train from Koblenz to Bingen and getting on your ship there. Ride the ship to perhaps Boppard and then train back to your final destination for the night. Trains run more frequently than the ships, so you will find that using a ship as a hop on hop off form of transport to not be ideal. Lots of time spent docking, undocking and if you only have 1 day, this may be a bit frustrating.
Which museum in Bingen did you want to visit?
"I want to take a Rhine cruise from Koblenz..."
Ms Jo is SO right. Travel first to Bingen by train - get off and on in the villages as you go - then cruise back; starting a cruise in Koblenz means SIX HOURS on the boat and some relatively dull scenery before you hit the interesting part. The more efficient Bingen-Koblenz cruise instead would cost you only about 3.7 hours. But again, the interesting scenery is pretty much over with well before Koblenz- so cruise no further north than Boppard (about 2.3 hours) and you'll have more time to pack it all in. You could shorten it even more and end the cruise in St. Goar (1.5 hours) and still have a nice cruise.
So... I would get on a morning train from Koblenz to Boppard or St. Goar and drop bags at a hotel there (maybe look into Schloss Rheinfels.) Use the train to visit Boppard, St. Goar, Oberwesel, Bacharach, and/or Bingen. Then catch the 14:30 or 16:30 cruise boat back to your home base.
If you want to just TOUR a castle, then the obvious choice from Koblenz is to hop on a southbound train for 11 minutes to Braubach for a tour of the never-destroyed MARKSBURG.
I'm just starting the research but I'm a huge Hildegard fan and read there's a museum for her in Bingen. Other than that I want to see the castles on a cruise and stay in a castle.
There is a castle-hotel in Kaub - Gutenfels. You could drop bags there, take the train to Rüdesheim, ferry over to Bingen, then cruise north in the afternoon from Bingen to St. Goarshausen (across the river from St. Goar on the same side as Kaub) and then train south 10 min. from St. G'hausen to Kaub.
Photo of Burg Gutenfels Hotel above Kaub and the Pfalzgrafenstein Castle:
You can also look at Hotel Castle Leibenstein, rooms from 130 euros or the Bacharach Youth Hostel. [Hotel Kranenturm](www.kranenturm.com) is not a castle, but it does have rooms in its tower. Rick's Germany book has specifics for his favorite towns along the Rhine, plus a narration of some sites you'll see from the boat. You can also get a taste of the region (but not specifics) at http://www.ricksteves.com/europe/germany/rhine-valley.
As close to a castle as you can get is Hotel Kranenturn in Bacharach--built in the late 1500's. Kurt and Fatima are great hosts, and he has a very good restaurant. There is a train stop in Bacharach, but unfortunately the express trains run outside Kranenturn's back door at night (loud.)
I'd suggest you also look for accommodations on: http://www.bensbauernhof.com/accommodationsrhinemosel.html