In 1894, the Art Nouveau enthusiast and millionaire industrialist Armand Solvay commissioned Victor Horta to build him a huge mansion on the fashionable Avenue Louise. Having developed a friendship with Horta and a close understanding of his requirements and preferences, he gave the architect carte blanche and an unlimited budget. Horta did not disappoint his friend and channelled his design genius into what is considered by many to be his masterpiece. The façade features two symmetrical, two-storey bay windows, topped with balconies. Inside, Horta used expensive materials to decorate an airy interior that could be adapted for entertaining and family life. Horta used 23 different types of marble and 17 varieties of wood in a decorative scheme dominated by red and orange tones that reinforced the luxurious atmosphere. The interior has been remarkably well-preserved and maintained and the building is a UNESCO World Heritage Site. Children under 12 years of age are not allowed.