This is a photo tour of Sankt Goar, which sits below the ruins of Rheinfels castle. Rheinfels was the largest castle on the Rhein, until Napoleon's troops mined and blew it to pieces. Sankt Goar is close to Frankfurt and Weisbaden, a little over an hour away. There are approximately forty castles within an hour of Sankt Goar, making it an ideal center for visiting the medieval Rhein / Rhine river area.
There are other places to stay, and I know Rick Steves recommends the city Bacharach, which is a nice place too, but I liked were we stayed -- it was central (if you have a car), clean, and very cheap. I paid EUR33/night for a single room with a large private bathroom, a small balcony, and a decent breakfast. The place I stayed was Hotel Keutmann, and I intend on staying there again when I go back to see the castles which I missed. Parking was ample and free. There is a restaurant on the premises which was just as good as the overpriced touristy places in Sankt Goar, and the hotel is almost directly across from the Lorelei rock, which is kind of cool.
There is also a hotel actually inside the Rheinfels castle which looks nice as well -- I tried to book it at first but it was full. The prices are reasonable for such a place, though of course quite a bit more then Hotel Keutmann.