Have you ever heard of the world’s deepest hole? I just found out about it a short while ago, and I have to say it’s quite a fascinating story. In the Murmansk region of Russia, there is a well sealed with a rusted metal cover. Under that cover lies the Kola Superdeep Borehole—practically the deepest hole in the world, drilled down 12,262 meters into the planet’s interior.

The interesting part is how they managed to get there. In 1970, they began drilling with the ambitious goal of penetrating the Earth’s crust and reaching the mantle. The first few kilometers seemed promising, almost easy. But then things started getting strange. At seven kilometers deep, they found water where, in theory, there shouldn’t have been any. Even more absurd: at nine kilometers, they discovered fossilized microorganisms that are two billion years old. Geology textbooks had to be completely rewritten.

But the real chaos came at twelve kilometers. The rock temperature reached 230°C instead of the 100°C that everyone expected. At that depth, the rock no longer behaved like a solid, but like a dense, plastic mass. The drill string got stuck and snapped. They had to start over multiple times from new lateral branches. It was the most expensive and frustrating project in the history of engineering. In 1994, they simply gave up. Money ran out, the technology was pushed to its limits, and the mantle was still 15–20 kilometers away.

Here’s the paradox of the world’s deepest hole: 12,262 meters sounds impressive until you realize that the Earth’s radius is 6,371 kilometers. We’ve penetrated only 0.2 percent. If you imagine the planet as an apple, the drill wouldn’t even have punctured the skin. Today, the well is sealed, the equipment has been stolen, and the surrounding buildings have collapsed. All that remains is a rusted cover and the silence of a rather humiliating reminder: we know less about our planet than we do about the surface of Luna.