When the drill reached 14.4 kilometers, it had broken through solid rock and into a large cavern that wasn't supposed to be there. From the surface, scientists could hear something coming from the hole. They lowered down an instrument array including a microphone. There was air in the cavern nine miles beneath the surface, but it was mostly toxic gas and the air temperature was over a thousand degrees. None of this made sense. They turned on the microphone. What they heard caused most of the crew to quit on the spot. For the few that remained, it only got worse. They called it the well to hell.