A visitor on a Botswana safari holiday will soon realise why the Tswana word for rain - 'Pula' - is also the name of the national currency: this is a sun-baked, arid land where water is as precious as the diamonds upon which its wealth has been built. It's also home to some of the world's greatest wildlife destinations: the Chobe National Park , where the ground literally rumbles beneath the feet of thousands of elephants.