The Burg Sonnenberg Castle dates back to the year 1200 and secured the area north of Wiesbaden for the Counts of Nassau.
It was the most important bastion of the dukes of Nassau. Duke Adolf, who was elected German king in 1292, resided here.
Today the citadel is an imposing ruin. The tower, which has been preserved, houses a small museum. From the tower and the restaurant terrace, the view sweeps over the valley and across wooded hillsides.