The oldest part of the present Bossenstein Castle is the square keep, probably built before the 14th century by a Joannes van Busco or Van den Bossche. Not much later it went to the Van Berchem family. They are supposed to have made some major alterations to the castle. They sold it in 1544 to Guilelmus van der Rijt, who was a member of the city council of nearby Antwerp. In the deed of sale the castle was described as an impressive estate, with a lot of outbuildings. Of these outbuildings nothing survives.
In 1655 it was sold again, this time to Willem van Halmale. He rebuilt the castle into a beautiful residence, which was still fortified. During the 18th century the castle changed hands several times between several noble families. Between 1798 and 1843 the castle was used by religious institutions. In 1906 the castle underwent restoration works, saving it from slow decay.
At present the castle is surrounded by the grounds of an 18-hole golf and polo club. The terrain of this club is probably not freely accessible. There is however a long distance walking path leading through the golf course which is. As far as I know the castle itself can not be visited.
References:The Château Royal de Collioure is a massive French royal castle in the town of Collioure, a few kilometers north of the Spanish border. The Château is the juxtaposition of at least four castles. Roussillon was conquered by the Romans around 120 BC and then occupied by the Visigoths from 418. The first mention is about a fortified site in Collioure under siege in 673, by Wamba, king of the Visigoths who lay siege to the “Castellum Caucolibéri” to subdue a rebellion.
In the 12th century, Girard II, the last independent count of the Roussillon, bequeathed his land to Alfons II, King of Aragon and Count of Barcelona. Concerned about the prosperity of Collioure, the kings of Aragon granted privileges and tax exemptions. An annual fair was established, and important works were undertaken in the castle, the port and the town.