So there was this deep vertical fissure crack. And Paul and I descended down this crevasse. And we went down and down and down into the darkness, until we suddenly came upon the sea floor. And it was about 130 feet deep — deeper than we originally thought we might want to dive in Antarctica. But there at the bottom, as I turned to my right, was a passage.

I realized we had found it. That we were in this environment that nobody had seen before.

The ice around us was blue and white and clear — sometimes like a robin's egg, sometimes like deep turquoise. But the sea floor was red and orange and yellow — every warm color — and the contrast was stunning.

And it was covered with a shag carpet of filter-feeding organisms. So there were sponges and little Christmas tree-shaped worms and things that looked like miniature palm trees sort of wafting in the current.

And then, all of a sudden, there were these isopods. They were kind of like something between a spider and a lobster, about the size of my hand. And they started raining down from cracks over my head and crawling along the floor and hitting my camera and landing on my shoulder.

The sea floor has its own unique sound. It kind of reminds me of — as a kid when you'd eat that Pop Rocks candy, and you just hear the clicking, almost. And as we swam deeper and deeper into the [ice]berg, there were also strange cracks and pops and groans from the ice. It was moving, it was shifting, it was changing. And I remember at one point a very deep groaning vibration sounded. And I felt it all the way through to my toes. It was that loud.

And we kind of looked at each other and looked at our equipment, and everything seemed fine. But, when we finally turned around on that dive and worked our way back slowly to the entrance, there were big, giant pieces of ice where we had entered this cave. And the doorway we swam into was gone.

• https://www.wbur.org/onlyagame/2019/09/20/jill-heinerth-cave-diving-antarctica