During the Cold War, the Unites States and the Soviet Union raced to see who would reach the moon first. But they also competed going the other way -drilling down through the earth. Both countries wanted to bore all the way through the Earth's crust to reach the mantle. The Soviets went down seven miles, and dug the earth's deepest hole.
Read how they did it at Wired. http://www.wired.com/science/discoveries/multimedia/2008/08/gallery_kola_borehole
At the Kola Institute, pictured, the Russians drilled for more than 15 years to reach a crust depth of 40,226 feet, a record that's never been broken. But however successful the mission was as an exploration, the geological findings from the site remain murky and obscured by the way they emanated out of the fading Soviet scientific machine.
Stanford geologist and drilling expert, Mark Zoback, said that the Kola borehole was "an anomaly" even within the rather grandiose field of superdeep drilling projects.
Read how they did it at Wired. http://www.wired.com/science/discoveries/multimedia/2008/08/gallery_kola_borehole
Deepest Hole
Yo mama