Nigeria, Nov. 24 -- It's almost noon, and the swelter tells the rest of the story of Limpopo, South Africa's tropical province. Just two hours ago, we were departing Johannesburg, a bustling jungle of sky-smooching shiny buildings. That frame has now given way to sweeping savannah views on either side of N1. This well-maintained highway stretches for 2,000km, from Cape Town via Johannesburg to Polokwane, then on to little-known Musina, a border town sandwiched between the Tropic of Capricorn and the Limpopo River.

Flanked by Botswana, Mocambique and Zimbabwe - on three sides of the eponymous river - Limpopo is easily accessible with regular flights and buses between Johannesburg and Polokwane, the provincial capital, and secondary towns....