Gutenfels and the Pfalz
The Pfalz is unique, being a castle in the middle of the Rhein.  Tours are available, and you can walk the inner courtyard.  This fortress, designed as a toll booth, was built to be flooded.  During the high water season, the inside courtyard is flooded, and men would walk the perimeter of the castle, staying high and dry.  Unfortunately, there was scaffolding and a green net around it, marring any photos in 2005.  This was gone in 2007, and I could get some good photos then. 

Right, a picture I took back in 1978.  Below, two photos I took in 2007.  On the left is the up river, or "prow" of the castle.  Note Gutenfels in the background.  On the right is the down river view.
To the lower left, a close up shot of one of the wall turrets.  This portion of the structure is made of wood and overlayed with slate siding and shingles.  While the slate adds some protection, this would be modest, and thus these types of turrets are more for observation than as fighting posts.  The floors are wood, and are only reinforced by several wooden angle braces.

Below, a close up of the coat of arms of the family that owned the Pfalz.  This close up is an enlargement from another photo, which demonstrates the quality of the Minolta A100.