During the Cold War, Soviet engineers drilled the Kola Superdeep Borehole on Russia’s Kola Peninsula. It is the deepest man-made hole, going about 12,262 metres (40,230 feet) down. That is deeper than Mount Everest and the Mariana Trench are tall or deep. The goal was to study the Earth's crust and learn about its structure, earthquakes, volcanic activity, and early life. The hole is just 9 inches wide and was drilled from 1970 until 1992. Despite many challenges, it remains a scientific marvel. The drill reached about a third of the local crust but never reached the mantle. Extreme heat around 180°C (356°F) and unstable rock that behaved like plastic stopped the project. The fall of the Soviet Union also ended funding. The hole revealed surprising findings. Scientists expected to find a change from granite to basalt rock inside the crust, but the rock stayed granite-like much deeper. They discovered salty water in cracks miles underground. They also found ancient microscopic fossils about 2 billion years old. The Kola Borehole taught us that Earth's crust is hotter, wetter, and more complex than thought. Although the hole is now sealed with a simple metal cap in a rusty yard, it stands as a Cold War scientific milestone. Future drilling may go deeper to reach the mantle. But for now, Kola holds the record as the deepest hole ever drilled by humans.