Tucked away in the old cellars of Bercy in the heart of the 12th arrondissement of Paris, the largest private collection devoted to shows and fairground art comes alive during the end-of-year celebrations. The Festival du Merveilleux is open to the public until January 2. And this year, it is placed under the sign of the Roaring Twenties, the name given in France to the decade from 1920 to 1929, which thirsted for freedom and modernity.