Katzenelnbogen is the name of a castle and small town in the district of Rhein-Lahn-Kreis in Rhineland-Palatinate, Germany. Katzenelnbogen is the seat of the Verbandsgemeinde Aar-Einrich.

Rheinfels Castle is a castle ruin located above the left (west) bank of the Rhine in Sankt Goar, Germany. It was started in 1245 by Count Diether V of Katzenelnbogen. After expansions, it was the largest fortress in the Middle Rhein Valley between Koblenz and Mainz. It was slighted by French Revolutionary Army troops in 1797. It is the largest castle overlooking the Rhine, and historically covered five times its current area.