Some days deliver the unexpected in the most exquisite way.

We had calm sea conditions all morning but with a significant open ocean swell. Despite this, we got a call after lunch that the ship would try out “an idea.” The idea turned out to be an open water swim in the deepest known part of all the world’s oceans. We were above Challenger Deep, part of the Mariana Trench that reaches a depth about 10,935 meters (35,876 feet).

Don Walsh and Jacques Picard made the first submersible dive here on January 23, 1960, in a two-meter diameter bathyscaphe called Trieste. Nobody would attempt the dive again for 52 years.

On National Geographic Resolution, the captain and bridge team used dynamic positioning at 11° 22.4’ N, 142° 39.2’E to keep us in one spot, and they angled the ship for safe transfer into the Zodiacs. We drove away from the ship, and then we jumped in.

The water was a deep blue-turquoise with astonishing clarity. We lowered weighted strings down 85 feet to observe just how excellent the visibility was. Some of us dove down a little, but there would be over 10 kilometers to go before reaching the bottom.

As I swam, I looked to the Zodiacs around me to see people floating, waving, whooping, and simply staring straight down into the warm, clear, and profound power of the ocean. It was both thrilling and intimidating.

The rest of our day was pleasant and interesting. Our time floating above Challenger Deep was unforgettable.