Originally Posted by
vendsit
The train is 6 hours and I don't want to waste a good portion of a day on it.
What makes you think the train is 6 hours? It is actually 4 hours, which makes it competitive (time wise) with flying.
But for your trip I would suggest that after Amsterdam you take the train as far as Cologne (as suggested) and then rent a car from there to explore the Rhineland, which has quite a few interesting and scenic places on offer.