The Kola Superdeep Borehole, dug during the Cold War ... What secrets were uncovered miles beneath the Earth's surface? Watch to find out! OPM tells government agencies to start firing recently ...

Your first challenge would be digging through the Earth's crust ... That point is at the bottom of the Kola Superdeep Borehole, at 12,260 meters below the surface. Down here, there's 4,000 ...

During the Cold War, the US and Soviets both created ambitious projects to drill deeper into the earth than ever ... Find out more about the Kola Superdeep Borehole in this BBC Future article.