In 1919 the pond is excavated. The plan is to make a large round pond that becomes a small waterway. But the oxidized iron layer in the ground is damaged during the excavation work. Normally, the iron layer prevents the rainwater from seeping away, but now the pond runs empty time and again. After countless attempts to repair it, an artificial bottom is installed with rolls of mastic (asphalt), which are rolled out across the entire floor of the pond and attached to each other with tar. The bottom has been waterproof ever since.
As a precautionary measure, a windmill designed by Henry van de Velde is placed near the pond in 1921. This is intended to pump up groundwater to maintain the level of the pond in times of drought. The windmill was never needed and was later removed, but the base structure under the mill has been preserved.
The reliefs by Joseph Mendes da Costa represent the old and the young Hubertus; the appearance of the crucifix to Hubertus and the moment that he takes up the crucifix and carries it on through life.
Helene asks the artist Arthur Henning to make a stained-glass window for the large window in the entrance hall of St Hubertus. The window, which depicts the legend of Saint Hubertus, is not installed until the 1920s.
Design for the 'bay window in Madam's sitting room' by H.P. Berlage