The town of Carletonville, South Africa, sits atop one of the most extreme frontiers of human endeavor. While the surface appears as a typical mining hub in the West Rand of Gauteng, the world beneath it plunges to depths that challenge the very limits of biology and engineering.  Image(Created) : The Go-To Guy At the heart of this landscape is the Mponeng Gold Mine, which holds the undisputed title of the deepest operational mine on Earth, reaching more than 4km (2.5miles) b