Rhine Castle

"There are no "authentic" castles that you can stay at in that area." You can have your "authentic" experience, I'll take modern bedding and flushing toilets over straw and privy pots any day! Want a little plague with that as well?

There are no "authentic" castles that you can stay at in that area. There are some hotels that have been rebuilt on the site of a former castle to look like a castle. Schönburg in Oberwesel is one, but I would call it crazy expensive. Stahleck, in Bacharach, is a hostel. There is also a four star hotel, Romantik Hotel Schloss Rheinfels, built next to Rheinfels castle in St. Goar.

True, the castle-hotels along the Rhine are not "authentic," but they offer better views and less noise and congestion than anything along the river. I have considered staying there a couple of times, but the prices and mixed reviews on TripAdvisor have kept me away. There are alternatives, however. For a listing of castle hotels and wannabes in Germany, see http://www.germany-castles-hotels.com/ Depending on where you are coming from, you might want to look at castles with hotels in neighboring countries. We have stayed at the historic castle in Sedan, France, and I would definitely recommend it, and especially the restaurant.

Burg Stahleck is a really nice hostel. It's very clean and quiet, but the beds (that I've seen) are single beds or bunk beds. It's always full so you need to book ahead. If it's available, they can give your group a room together sharing a dedicated bathroom. We had the Rhineblick room for our family. The room had a view of the castle courtyard and Rhine. Koblenz has a similar hostel, but I've never stayed there.

http://www.rhinecastles.com/