2Kola Superdeep Borehole (12,262 meters)

In Russia, the Kola Superdeep Borehole is Earth’s most bottomless artificial hole. Scientists began drilling it in 1970 to study the Earth’s crust. Although it measures only 9 inches wide, it reaches a depth of 12 kilometers!
Scientists only penetrated a fraction of the Earth’s crust despite its incredible depth.