For most people, completing the "Explorers Grand Slam," which requires climbing the Seven Summits — the highest mountain in each of the seven continents — and reaching the North and South Poles, would be achievement enough. However, not for American explorer and adventurer Victor Vescovo, who completed the challenge in 2017. Since December 2018, the 54-year-old former US naval officer has been on a new quest — to become the first person to take a manned submersible to the deepest-known point in each of the world's five oceans.