The Bourse de Commerce, Piazza Pinault in Paris

On-and-off showers soaked the forecourt of Les Halles, where three flags, as gray as the sky, were flapping in the wind. Their light, seemingly liquid fabric looked like molten metal in the chilly air. Halfway between the Louvre and the Centre Pompidou, the Bourse de Commerce looks like an ancient UFO. After a three-year facelift, it is the new public home of a private passion, that of French billionaire François Pinault ( editor's note: founder of the companies Artémis and Kering ) for contemporary art, whose collections have been on view in Venice at the Palazzo Grassi since 2006 and, later, at the Punta della Dogana . Historic sites suit this rich, discordant collection of over 10,000 contemporary works made by 400 artists since the 1960s. Two hundred selected pieces are on display beneath the skylight of the former commodities exchange. "François Pinault was here every day during the installation,” says Caroline Bourgeois, curator of the billionaire’s collection and a member of his inner circle. “It reflects his personal…