
Deep in western Russia, if you know where to look, you’ll find a small collection of ragged scrap metal and crumbled concrete. Which isn’t that exciting.
But if you rifle through the rubble, you will find a large metal disc bolted to the ground. This isn’t just any old disc – it’s the welded-shut cap of a borehole that plummets more than 12 kilometres (7.5 miles) into the Earth.















