When the crew aboard the S.A. Agulhas II set out in early 2022 to search for the Endurance shipwreck, it seemed nearly impossible.

“It’s the holy grail,” Nico Vincent, the sub-sea manager on the expedition, tells Variety. “It’s the most complicated one. Just being able to reach the field and dive three kilometers beneath the ice, it’s the level of complexity of walking on the moon.”

The Endurance, commanded by explorer Sir Ernest Shackleton on an expedition to traverse Antarctica from one coast to another, sank in the Weddell Sea in November 1915 as its 27-member crew looked on. Over the next 308 days, the men faced starvation and frostbite as Shackleton recruited five crew members to make the treacherous journey in a lifeboat to seek help on the South Atlantic island of South Georgia. Miraculously, when Shackleton returned to save the remaining men, he found all of them still alive.