In summertime heat, our minds drift to the ocean—and, this week, we’re bringing you stories about exploration, danger, and discovery on the high seas. In “The Squid Hunter,” David Grann sets sail with the marine biologist who will brave any storm to sight a living giant squid; in “Secrets of the Deep,” John Colapinto investigates the dispute over a vast sunken treasure that may be the largest ever found. The long-distance swimmer Lynne Cox describes swimming the Northwest Passage in “A Dip in the Cold,” and, in “The Crossing,” Alec Wilkinson meets an eccentric adventurer determined to undertake a trans-Pacific voyage on a homemade raft. Elizabeth Kolbert explains what it will take to save the world’s coral reefs in “Unnatural Selection,” and, in “Her Deepness,” from 1989, Wallace White profiles Sylvia Earle, the intrepid marine botanist and deep-sea diver who—after living in an underwater laboratory and visiting the ocean floor in an experimental diving suit—became the first woman to hold the position of chief scientist at the National Oceanic and Atmospheric Administration. We hope that you enjoy these voyages beneath the waves.