When driving to Germany you will have to deal with environmental zones (umweltzones). You are only permitted to drive in these zones when having an environmental sticker(umweltplakette).
To visit Van der Valk Düsseldorf you do not need an environmental sticker. However, if you want to visit the center of Düsseldorf and drive by car there, then you are required to have such a sticker on your car. It is advisable to already order your sticker in your homecountry.