Thurant
Burg Thurant is a unique castle in many ways.  Its location also makes it easy to miss because it is so high above the Mosel that you can drive right past it (I did).  I only spotted it when backtracking looking for another castle.  Thurant was built in the 1190s, and was soon owned by two of the Catholic electors in the Holy Roman Empire, the Archbishops of Cologne and Trier.  These two disliked each other sufficiently to have a wall errected in the middle to divide the castle in two.  The castle would manage to survive through the middle ages, but would fall into disrepair in the 1800s.  It was rebuilt some in the early 1900s and has some delightful artifacts on display.  A further plus is that it has a self-guiding tour.
Thurant stands out above the Mosel River and is easily accessible by road.  The entrance below sports a nice portculis, while the castle also has a small summer apartment that can be rented.