Kola Superdeep Borehole

The Kola Superdeep Borehole SG-3 is the result of a scientific drilling project of the Soviet Union in the Pechengsky District, near the Russian border with Norway, on the Kola Peninsula. The project attempted to drill as deep as possible into the Earth's crust.

Drilling began on 24 May 1970 using the Uralmash-4E, and later the Uralmash-15000 series drilling rig, and it became the deepest man-made hole in history in 1979. The 23-centimetre diameter boreholes were drilled by branching from a central hole. The deepest reached 12,262 metres in 1989, the deepest artificial point on Earth.

Source: Wikipedia