Discretion is paramount here. "German clients tend to be rather reserved when it comes to luxury, whereas foreign clients like to show off what they have," says Jürgen Willen - and he knows what he's talking about. On almost every continent, the architect and his team design luxury villas and interiors for a clientele seeking something truly unique. From bathtubs to car lifts with washing facilities, if it's on the wish-list and can be done, Willen will make it happen. Mira van der Zalm's client base is equally discerning. The estate agent arranges the sale of houses and flats not advertised on the open market - that takes a special level of service. For example, she calls in Jürgen Willen to an Art Nouveau villa in Wiesbaden to check whether it's possible to install an underground parking lot and a spa - and if it can be done in accordance with listed building regulations.