The Kaja ruins, Niederfladnitz Castle and Karlslust have been owned by the Waldstein-Wartenberg family since 1945. Niederfladnitz Castle is partly owned by the municipality of Hardegg.
About history:
1279 an Otto de Vlednitzer is mentioned. In 1425, Duke Albrecht V. left the dominion of Kaja, which also included Niederfladnitz, to Ulrich von Eyczing.
At the beginning of the 16th century, the Eyczinger moved their residence from Kaja Castle to Niederfladnitz. For this purpose, they had the manor expanded and made more comfortable. However, they saw the castle more as an administrative seat than a representative building. In 1615 Niederfladnitz was inherited by the Trautson family as part of the Kaja dominion. She also sees the building as an administrative headquarters and not as a residence.
In 1775 the family of the princes Auersperg inherited the dominion with Niederfladnitz Castle and Kaja Castle. Prince Karl Auersperg-Trautson (1750-1822) built a representative hunting lodge near Niederfladnitz with Karlslust around 1800. The old castle remains the administrative seat. After the death of Prince Franz-Joseph Auersperg (1856-1938), the property first passed to the Croy family via his daughter Christiane, and then to the Waldstein-Wartenberg family. In 1944/45, Jewish forced laborers from Hungary were used to work in agriculture and forestry.