After the huge success of recent shows in Venice, London and Paris, interest in Outsider Art has never been higher. But what exactly is it? How do we define it? And who are its gurus and leading lights? Alan Yentob explores this captivating, compelling and magical alternative art universe. Why in 2013 is Outsider Art finally being feted by the art establishment, and what took it so long? imagine... embarks on a worldwide journey to meet some visionary creators, and their equally obsessive collectors and enthusiasts.