The Tropic of Cancer runs through 17 countries and Simon Reeve visited most of them - and one or two others for good measure - on a journey round the imaginary line. He found a huge variety of climates and landscapes, from deep jungle to vast desert, and an even bigger range of ways of life, from deep poverty to vast wealth. He talks to Sandi Toksvig about his experiences, including sneaking illegally into Burma, and what conclusions he has come to about the way the planet is changing.
The port of Darwin in northern Australia and the region behind it known as Arnhemland is one of the less touristy parts of the country. But it has much to offer in terms of an impressive terrain that hasn't altered for millions of years and which has been home to the aborigine people for many thousands. Sandi talks to travel journalist Wendy Gomersall, who has visited the area and the indigenous people, and Sab Lord, who was brought up there on a buffalo station in what is now a national park the size of Wales and who acts as a guide to the area's natural and human heritage.