Furstenberg
While the tower is closed, you can access most of the rest of the castle.  You can walk the ruins and just imagine how it once looked.  The ruins attest to the strength of this once mighty fortress.
A portion of the curtain wall shows that it was built along with a portion of the rock.  Below is the interior of the tower, which is closed off above.

Lower right... a view up the valley toward Ober-Diebach, looking to the southwest.