Falkenstein and Burg Nurings
There is not much left of Falkenstein, the neighbor to Konigstein.  It is mostly a few ruined walls and the central keep.  The keep does provide a fabulous view of the Hoch Taunus and of Konigstein, though the poor weather in 1977 made for equally poor images.

Crawling around the castle were a group of "gemsbok"... rams... who were the only residents now extant.  By and large they were friendly and mild and I even petted one.  Gemsbok were no longer present when I went to the site in 2012.
The origin of the castle remains obscure, with early mention of the site in the 1200s.  The same family that controlled Konigstein controlled Falkenstein at this time.  In 1364, the castle was destroyed.  Rebuilt, the castle was used as a haunt for robbers at one point before another noble family controlled it.  Damaged during the Thirty Years War, the castle was allowed to slowly languish and fall apart, with local villagers occupying those structures still inhabitable.  The imperial family of Bettendorf received the castle at the hands of the counts of Nassau-Saarbrucken and were such harsh rulers that the local people sacked the castle and tore down the walls, using the material for local building projects.  In the mid-1800s efforts were made to stop further destruction and by the 20th Century the castle passed to the state of Hesse.

About all that really remains of Falkenstein is the keep, which has been restored.  Update: see the next page for more recent photos from 2012 showing restored areas.
Left, a view of Konigstein from Falkenstein during misty winter weather in 1978.
Cold and dank, Konigstein rises from the mist.  This view was from the section of the town just below Falkenstein.