Olbruck
Olbruck is actually a very nice castle to visit, and there is much more there than just the large keep, though this is impressive enough.

The keep can be seen for miles around as seen in the photo below.

These photos were taken in 2008.
Olbruck was first mentioned around 1050 when the early castle was built out of a basic motte and bailey hillfort.  The Olbruck family held it until 1196, when the castle passed to a female heir who married into the Epstein family.  Various marriages and disputes placed ownership of the castle in doubt for several hundred years.  Lords from as far afield as the Rheinland and Trier contested ownership and made claims and counterclaims.  During the Thirty Years War the castle was besieged and destroyed by Swedish troops under Heinrich Baudessin  in 1632.  Rebuilt, the castle was destroyed by the French in 1689, but reconstruction began again one year later.  By the mid-1700s the castle was no longer used as a residence and was largely abandoned with the reconstruction work unfinished.  By 1815, it became state property but was again transfered to private ownership by the 1870s.  After passing through the ownership of several families restoration began in the 1970s with focus being on the keep.
Above left, a close up of the keep.  Above, a model of the motte and bailey hillfort that preceded the current extant structure.

Left, part of the turret that guarded the main gate.