My wife and I are flying into Amsterdam on 3/21 and gonna spend a few days there before making our way to Frankfort for our return flight on the 28th. I was able to convince her to get a car as we usually just get a rail pass. She's not too keen on driving because she usually has to have the trip planned out to the minute and wants to know where we're going to stay every night before we leave. I'd like to stay in Amsterdam for a couple of days and work our way through the countryside and stop where and when we want as long as we end up in Frankfort on the 26th. She did want to go to Berlin but I don't see this as possible unless we fly there the morning of the 24th and then rent a car and drive to Frankfort. The train is 6 hours and I don't want to waste a good portion of a day on it. Any suggestions on route, sites to see, places to avoid would be appreciated.

I've been checking on a one way rental car on my US based accounts with no luck. Does National or Hertz not do one way rentals if you cross borders? Do you have to use a European based rental company? I checked on one site and it offered a Hertz rental but I'd like to use the 5 free days I have if I can.

Thanks in advance for any help or suggestions.