Saturday, 8.30pm, BBC Knowledge This terrific Canadian series looks behind the entrance doors of some of the world’s most famous museums to unveil little known facts about some of the treasures they contain that the casual visitor would miss. In the coming weeks, we’re walked through the fabulous collections of Washington’s Smithsonian Institution, Paris’s Chateau de Versailles, the Israel Museum in Jerusalem, Royal Museums Greenwich, Florence’s Uffizi Gallery, Tunisia’s Bardo and the State Historical Museum, Moscow. In this episode, secrets of Madrid’s Palacio Real are revealed through interviews with curators and historians, and reenactments. It starts by exploring the origin of Spain’s splendour and power in the 16th century. No, it wasn’t due to gold or silver but mercury. Through the centuries, more than millions of miners died from the toxic vapours while many more went insane. Still, they made the Palacio’s magnificent hall of mirrors possible.