The deepest man-made hole on Earth is no longer a gaping wound in the Arctic rock but a quiet, sealed scar. Once hyped as a literal “entrance to hell” in feverish urban legends, the Kola Superdeep ...

Beneath our feet is an almost limitless source of energy, but while a few lucky locations have geothermal heat close to the surface, the rest of the world will need to dig a lot deeper. The challenge ...