The remains of the Castle can be visited
Steinsche Castle

The Steinsche Burg castle ruin, a hilltop castle, is located near the town of Nassau in the Rhein-Lahn district. It was the ancestral seat of the Imperial Barons vom und zum Stein, a family first documented in 1158, which included the Prussian reformer Heinrich Friedrich Karl vom und zum Stein. Its position below Nassau Castle made it an important advanced fortification.
History+
The exact construction date of the castle is unknown. The vom und zum Stein family held the complex as a fief from the Counts of Nassau, with its primary function being to protect the main Nassau Castle.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=932
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 50.3133, 7.7908