Based in North-western Russia, the Kola Peninsula project Kola Ultra Deep commenced in 1970 and went on until 1992.
This is known as one of the most ambitious science experiments ever performed. At first it was an America and Russian 'race to the centre of the earth', unfortunately for America, they tapped out in the 1960's, a decade later Russia embarked on their journey and unfortunately they had to stop when the drill surface became dangerously hot.
Although the location is in ruins now, the hole still exists, its just covered with a heavy steel manhole cover bolted to the earth that covers a hole that goes 12km into the earth, deeper than the deepest depths of the ocean.
It's called the Kola Superdeep Borehole and funny enough it has nothing to do with petroleum exploration, but rather to gain a better understanding of the nature of the Earth crust. Russia had a goal of going as far as 15,000 metres. Because why not learn more about what is underneath our feet? In fact, we know less about it than we know about our own solar system, and that's trillions and trillions of recurring metres away. When drilling eventually came to a halt the Russians managed a record depth of 12,262 metres.
What did they find? Well, there's water down there, also microscopic fossils, 24 species of single-cell plankton microfossils up to 6.7km down. When the Russian Scientists reached the 12 km mark, rock samples were dated 2.7 billion years old, after that, the heat became a major issue, the researches thought the temperature of the rocks would be about 100 degrees Celsius, but what they found were temperatures of an excess of 180 degrees Celsius.
Even though this was an achievement for mankind, the earth mantle doesn't even begin until about 35km below the surface. Scientifically this hole that took 24 years to drill made 0.2% of the way to the middle of the earth.