Drachenfels
Drachenfels is not much left to look at.  However, it has a number of legends connected to it that lends a mystique to the castle.  The lines of Lord Byron celebrating the castle somehow worked into the thought of the West, and Drachenfels gained fame beyond its current condition.  The castle bears the same name as the rock on which it sits, and a legend states that Siegfried killed a dragon on the rock, and hence the name.  While legend, as an historian I have learned that legends often have some measure of truth connected to them, and it is very possible that a warrior did kill some nasty creature in the area.
The legend has been celebrated in Richard Wagner's Nibelungen romantic opera.

Drachenfels is one of a string of small mountains dubbed "the Seven Mountains."  These were volcanic in origin.
Above, a nice view of the castle with a river tour boat heading up stream.  Left, a zoom shot of the main portion of the castle remaining, being a portion of the tower.  A hotel has been built nearby (seen to the right), and at least those who did this ensured that the colors and general motif did not distract from the view.