A grand mansion sits at number 5 Avenue Marceau, near the intersection of the fashionable Avenue Montaigne and on the north bank of the Seine. With its ornate cornices and mansard roof, the building is unmistakably a product of Georges-Eugène Haussmann’s renovation of Paris – the city planner nonpareil who, under the instruction of Napoleon III, brought air and light to the center of the French capital. In 1974, the fashion designer Yves Saint Laurent – with his partner in life and business Pierre Bergé – moved the headquarters of his eponymous couture house here, having outgrown their former premises on the Rue Spontini.

“Yves Saint Laurent was particularly fond of the ceremonial splendor of this building,” Bergé remembers. “For forty years I observed him drawing, toiling, fitting and fitting again; witnessing drawing give rise to the garment.”

Today number 5 is home to the Fondation Pierre Bergé - Yves Saint Laurent, which has maintained its mission statement of promoting and conserving Saint Laurent’s body of work since the couture house closed its doors in 2002. Although now 85, as the foundation’s president, Bergé comes to work here every day as he has always done, and has elaborate plans for its future. In the fall of 2017, two museums dedicated to Saint Laurent will open their doors; one on the ground floor of the foundation, and the second in Marrakech, where Saint Laurent and Bergé shared a home that once belonged to the painter Jacques Majorelle.

In the meantime, on what would have been Saint Laurent’s 80th birthday year, W takes a rare glimpse inside the designer’s sprawling archive, which comprises some 5,000 garments from the 81 collections he created between 1962 and 2002.