Hohenwittlingen
Hohenwittlingen is not a very spectacular castle, but the view from the tower is simply awesome!

The castle was part of a string of fortresses that dominated the Erms Valley near Bad Urach.  It was first mentioned in records around 1090, but was probably the extension of an earlier hill fort.  The castle survived a major siege in 1311 during wars with some of the free towns like Reutlingen, but was later damaged severely by a lightning strike in 1576.  By the end of the Thirty Years War in 1648, the castle was abandoned and began to fall into decay.

These photos were taken in 2007.
While the castle does not have much to see, it makes one wonder what is under the structure.  Many castles have casemates or other underground foundations with tunnels and storage areas, but once a castle fell into decay most of these gradually filled with water or the entrances collapsed.  Above, some of the outer rooms of the castle, while above right is he stairway leading to the tower.  To the right is a view from the tower towards some of the other remnants of the structure.  The castle has had some work done to keep it intact, but has had virtually no restoration work done.
The way to the castle is a bit odd.  There are two approaches.  One comes from the valley below, and the trail is actually quite treacherous in some areas, especially when wet.  The other is to approach the castle from behind and above on the hill on which it rests.  Drive through Wittlingen until you reach a small parking area.  Hiking to the castle is tricky from this direction because you will be on a small paved road that will take you by a somewhat elaborate residence.  This residence is actually part of what was Hohenwittlingen, but is not the castle proper.  Instead, before you reach the residence you must cut to the right into the woods and pick up a dirt trail there, which will lead you to the castle.  It too can be a bit treacherous when wet, so watch your step!
Above left, and left, two views of from the castle itself.  The view is simply spectacular.

The fortification itself is not much, and clearly relied on its inaccessible location to provide the essentials of its defense.  Moreover, there were no details of left of architecture or building design to see, which is unfortuante.