What does the Louvre look like without the public? For the first time, the world's greatest art museum lets a film crew, led by acclaimed director Nicolas Philibert (Etre et Avoir), behind the scenes to reveal a spellbinding secret world. As staff hang paintings and reorganise rooms, we discover a hidden city within a city miles of underground passages, reserves containing thousands of priceless treasures and chambers that are off-limits to visitors.