In Ways of Escape, one of his three books of autobiography, Graham Greene said that he found writing a form of therapy. “Sometimes I wonder how all those who do not write, compose or paint can manage to escape the madness, the melancholia, the panic fear which is inherent in the human situation.” Travel was another way of escape. It took him, among other places, to Liberia (described in Journey Without Maps), Mexico (The Lawless Roads; The Power and the Glory), and Sierra Leone (which inspired The Heart of the Matter). For a new five-part series, Radio 4 has sent writers to various outposts of “Greeneland” to follow in his footsteps. It opens tomorrow at 9.30am with Katy Watson retracing his route through Mexico in 1938, where he went to report on religious persecution by the authorities.