A cold, dark expanse lies more than a thousand meters beneath the surface of the open ocean. In this crushing, near-freezing twilight zone, sunlight is a distant memory, and the water pressure is enough to shatter bone. Yet, gliding silently through this hostile abyss is an ancient survivor: the leatherback sea turtle ( Dermochelys coriacea ). While reptiles are traditionally viewed as sun-loving creatures bound to warm shallows and terrestrial basking sites, this massive marine giant shatters all herpetological conventions by routinely plunging into the deep ocean to forage. Recent high-tech tracking expeditions have shed new light on these extraordinary deep-sea migrations. Utilizing state-of-the-art satellite telemetry and multi-sensor biologging tags, international teams of herpetologists and marine biologists have recorded leatherbacks diving to depths exceeding 1,200 meters. These deep-sea excursions place the leath...