Baldenau
Baldenau is unique in that it is a castle in a low-lying area and not on a mound or hill.  Many castles were built in this fashion but few survived as they were more accessible to the locals who pilfered the stone for their own projects once the castles were abandoned as unecessary or uneconomical by their owners.

Baldenau has a wet moat surrounding it, thus providing it with enhanced defense that it lacked by not being on a mound.  This makes the castle unique in that it is thought to be the only one in the Hinsruck with a wet moat.

These photos were taken in 2008.
The castle was built around 1320, the ownership to the Elector of Trier, Balduin of Luxembourg, confirmed by the Holy Roman Emperor in 1322.  The castle was built to mark off the boundary of the Elector's lands with that of the Count Sponheim.  Plans were made to build a town nearby but this was never carried out.  The castle was damaged by the Swedes during the Thirty Years War, but was rebuilt during the early 1650s.  The French destroyed the castle in 1689, the destruction so severe that the site was abandoned.
The moat (above) goes directly up to the castle foundation in some areas.
One aspect that made Baldenau unique was that a team of workers were doing some restoration on sections of the wall.  The base of the keep, which is not open as the stairs and platforms are gone, was used to store equipment.  To the right, a worker applies a cement past to the wall to hinder the effects of age that cause the structure to crumble.  For many castles the stones are authentic but much of the outer mortar is recent.  This does not negate the authenticity of the structures, but must be taken into account when examining the buildings and walls.  One consequence of such reconstruction is the tendency to smooth out broken walls, thus implying that they were much lower than they actually were.