We are landing in Munich, renting a car and flying out of Frankfurt. The plan for now is overnight/day in Munich, rent the car and head south toward the castle's, then head back north to Rothenberg and onto the Rhine region and Mosel region overnight near Frankfurt airport on last night. Any suggestions appreciated. Also, not finding the hotels too booked right now. Only have three nights booked so far, any problems just showing up at this time of year (6/25-7/4)?
Since you are renting a car may I assume that your are travelling as a group (how many) and not as a single person? Then consider that you are travelling during high season. While you will find "something" upon arrival in any of your tourist destinations the best deals and nicest locations are usually found by booking ahead. Especially if you are travelling as a group and not as a single or couple. "Just showing up" is certainly possible but most of the time it will cost you more - in Euros and precious vacation time spent on making arrangements. Travelling during high season I would recommend to prebook. Just make sure you understand the cancellation policies to be able to retain flexibility in your travel.
In terms of recommendations on where to stay I'd try to spend at least one night in a castle overlooking the Rhine. There are a few options out there from very posh (read expensive) beautiful hotels to some budget hostels. It's hard to recommend anything specific without knowing your budget.
FYI in Frankfurt on the 5th, is the European Ironman Championship, which means hundreds of thousands of visitors along with all the families of the participants. I think 500,000 descended on Frankfurt last year. So, 1: the hotels may be fairly booked up, 2: you will not be wanting to drive in Frankfurt or possibly anywhere near, due to the roads being blocked for the bike race. They start with swimming very early in the morning out near the airport, then the bike race and then the marathon takes place along the river running laps around it and the finish line is in the Römer square.
EDIT: I made a mistake on the date. It is the 5th. Sorry!!
Check the school vacation list for the various states you will be going through and be prepared for some possible large traffic jams on the roads. (each state has a different vacation schedule)
http://www.holidays-info.com/School-Holidays-Germany/2009/school-holidays_2009.html
Thank you so much everyone! I have booked a hotel (Ibis-FRA) near the airport as we have a mid morning flight and need to return the car. I also booked a night at a castle along the Rhine and I am going to try to book nights along the route I think we will travel. I found some "rick" b&b's/hotels that have good cancellation policies. Again, thank-you. We have visited 19 countries with our two children over the last 10 years (this trip is the first without them!) and I always find this web board to be so helpful, even for countries that Rick doesn't cover.
The Sheraton Hotel is located right at the airport, but they may already be booked up with such a large event in town. Depending on your departure time, you can spend the night in your Rhein area hotel and drive in the next day…1.5 hours. A couple of visits ago, I stayed the night in Rothenburg odT and drove to Frankfurt the next day (mid-morning) for an afternoon flight to Reykjavik. I enjoyed spending the last night in a smaller town and had enough time the next day to make it easy and doable. If you have a morning flight, however, this wouldn’t work.