The original castle of Idstein was built around 1170[1] on a rocky ridge in the centre of the Old Town. Within the inner bailey, only the bergfried, the old district courthouse, the 15th century gatehouse and the palas have survived from the castle.
In 1905 the schloss became a Convalescent Home for Members of the Royal Prussian Army.[3]
The upper bailey was demolished and the bergfried was nicknamed Hexenturm (Witches' Tower) in the 19th century.[4] There were witch trials in the early modern period in Idstein, but these substantially predate the name of this landmark. It is unlikely that anyone was ever accused or imprisoned in the tower for witchcraft. The nickname became widespread around 1900 with the publication of Die Pfarrfrau von Heftrich by Ottokar Schupp [de]. The Hexenturm became the landmark of Idstein.[4] At the base of the tower is a plaque in memory of the victims of the witch trials of 1676, listing the names of 31 women and 8 men[5] killed at the end of the rule of John, Count of Nassau-Idstein.[1]
After the First World War, French soldiers were housed in the schloss during the French occupation. In the Second World War, the schloss acted as a military hospital for reserves.[3]
Today the castle houses the Idstein PestalozziGymnasium. Both schloss and bergfried may be visited on request.[3]
A 20-metre-long stone bridge spans the neck ditch between the outer and inner baileys. To its right is a small Renaissance garden. Guided tours are offered with the guides dressed as gardeners of 1702.[6]