The sumptuous interiors contain fine furniture, paintings, tapestries, Córdoba leather wall hangings and objects collected by the Merode family throughout the centuries.
Across the Nete river there is a larger formal park (60 hectares) in the French tradition with a rectangular pond forming a large perspective.
It was built between 1909 and 1912 in a neogothic style by architect Pierre Langerock as the residence of one person, Countess Jeanne de Mérode.
She lived with her parents and siblings in the 'old castle' until the death of her brother, Count Henri de Mérode, in 1908.
The architecture of the facades was inspired by the early 16th-century late Gothic wing of the nearby abbey of Tongerlo.
Although both interior and exterior were executed in a historical style, the building contained many modern features that were very rare on the countryside at the beginning of the 20th century.
On the altar she kept her most important treasure, the famous Mérode Altarpiece by the 15th century painter Robert Campin.
Countess Jeanne moved back to the 'old castle' of Westerlo where she died on 1 July 1944, a few months before the liberation of Belgium.