The Tropic of Capricorn runs around the southern hemisphere for about 22,000 miles, crossing some of the most remote and unexplored regions of the world.
Following the success of BBC Two's Equator - which charted a 25,000 mile spherical journey around the world, along the dividing line between the northern and southern hemispheres - Simon Reeve has embarked on an epic new adventure.
The team at the tropic of Capricorn
In the first leg of Simon's journey across the Tropic of Capricorn starts in Namibia, on a remote beach in the Namib-Nauklaft National Park.
The spectacular desert scenery makes this area, like much of this huge country, a huge draw for adventure tourists.
Simon meets a tame Cheetah at an animal rescue centre
Simon's first stop is Swakopmund, Namibia's second largest city and a place with strong German connections, where Mein Kampf and photos of Hitler are still on sale in the local curio shop.
Namibia used to be a German colony and the country has a dark past - German colonisers killed tens of thousands of locals in a forgotten genocide, which Simon learns about from a local historian whose relatives suffered in German "concentration camps" in Namibia.
A memorial for the Herero Tribe, killed under German rule in Namibia
Following an amazing encounter with a pack of hungry cheetahs and a French conservationist nicknamed "Catman", Simon arrives in the capital Windhoek, where he meets prostitutes infected with HIV (Namibia has one of the highest infection rates in the world) and witnesses at first hand the growing influence of China in Africa.
Travelling across the vast interior of the country, he meets members of the Herero tribe, goes out on horseback to round-up cattle, and witnesses the Herero Holy Fire ceremony.
Botswana confounds many of the stereotypes of poor Africa.
Well-run, with cattle-patrols that keep stray cows off the roads, Botswana is making a fortune from tourism and a natural resource that never seems to lose its lustre.
Digging for diamonds is a serious business in Botswana
The world's largest diamond mine, just south of the Tropic of Capricorn, produces millions of dollars worth of stones every week, funding universal education and extensive healthcare.
The mining firm has forked out on anti-AIDS drugs to keep its workforce functioning in a country where HIV rates have rocketed up to 40%.
But not all Botswanans are benefiting from the national prosperity.
On the edge of the Kalahari desert many of the legendary San people - also known as the Bushmen of the Kalahari - have been moved out of the desert into depressing resettlement camps by a government that says it wants them to be part of the modern world.
The government has provided basic huts and schools for the San, who are among the poorest people in southern Africa, but many of the San are having difficulty adapting to the modern world.
In a spectacular journey into the heart of the Kalahari Desert, Simon seeks out the remaining San who are still living in the desert alongside their lion "cousins".
Some San have won a legal battle, and plan to return to live in their Kalahari homeland - but as Simon finds out, life can be tough in this beautiful, brutal environment.
Series Producer: Sam Bagnall
Presenter: Simon Reeve
Director: Sophie Todd