It all began at Karl Lagerfeld’s Left Bank apartment in 1997. The award-winning Japanese architect Tadao Ando was invited to dinner, and when he arrived, he met, there in the 18th-century entrance hall, the French financier François Pinault, a noted collector of contemporary art. “Was he aware that I would be there?” Ando muses now. “I am not sure. I sensed that Mr. Pinault might have asked Mr. Lagerfeld to introduce me to him, to understand what kind of person and architect I was.” The Pritzker Prize–winner transformed the historic Bourse de Commerce into a sublime Paris home for the Pinault Collection.