Lahneck
As you head north along the east bank of the Rhein, and just before you reach the confluence of the Lahn River, you find Burg Lahneck.  Lahneck was built in the 1200s as a northern fortress to protect the southern lands of the Elector of Mainz.  A customs fortress was later built along the river itself to aid in collecting tolls on the river.

Gradually expanded, and redesigned some in the 1400s to deal with the growing trend towards firearms, Lahnstein was finally smashed by the French in 1852.  Its archetectural style was transformed to Neo-Gothic, and is today open for tours. 

While I went for a visit of the outer fortifications, I just couldn't bring myself to do another "fuhrung!" 
To the left is the initial entrance into Lahneck.  Regarding the cars parked within, I simply don't remember if they belong to tourists or to employees working in the castle.  Usually such spaces close to the entrance belong to castle employees.
Lahneck has a nice chapel built within, and this is the outer view. Chapels within castles can be identified by the window styles, compared to the remainder of the windows in the structure.  The chapel itself is supposed to be worth the visit, but I just couldn't bring myself to do another tour.