The Kola Superdeep Borehole, although only 9 inches in diameter, holds the distinction of being the deepest hole, plunging to ... delving deeper than any other man-made structure.

America might have landed on the moon, but Russia drilled the deepest man-made hole on Earth. Since the early 1960s, scientists have attempted to drill down to the Earth's mantle. It took 20 years ...