The very deepest spot within it is the eastern pool of a valley called Challenger Deep, lying at 10,928m below sea level. It was here, in April 2019, that American private-equity millionaire Victor Vescovo achieved the deepest dive made by any human in history. It was part of his now completed mission – called the Five Deeps Expedition – to visit the deepest points of the world’s five oceans.

Victor’s vessel was a submarine called DSV Limiting Factor, a craft he had specially designed and built by Florida-based company Triton Submarines. “This submarine and its mother ship took marine technology to an unprecedented new level by diving – rapidly and repeatedly – into the deepest, harshest area of the ocean,” he said after returning to the surface. “We feel like we have just created, validated and opened a powerful door to discover and visit any place, any time, in the ocean – which is 90% unexplored.”