In the open ocean in the dead of night, a light-studded downline silently sinks a hundred feet into the water’s inky depths.

Minutes later, there’s a splash as divers plunge in too. Equipped with scuba gear, a bevy of lights, and waterproof DSLR cameras clipped to their suits, National Geographic‘s David Doubilet and Jennifer Hayes descend into a realm of the unimaginable.

“When you first get in, it is a galaxy of light,” Doubilet says of black-water diving. “You see fellow divers with their shafts of focusing lights and red lights: a galaxy here and a galaxy there.”

In the dark—whether it’s the Sargasso Sea of the North Atlantic or the tropical waters off Indonesia’s Raja Ampat archipelago—Doubilet and Hayes see things even many other marine biologists (Hayes is one) will never see. Black-water diving is “the equivalent of a marine ‘Sorcerer’s Apprentice,’” Doubilet says. “All strange things that are dancing around at night.”

The duo capture rare images of creatures in their larval forms and observe the clever ways the animals survive the night, like a juvenile jack that hides behind a jellyfish. But as the current propels them through the sea, divers must keep an eye on their bubbles to remember which way is up—and on the downline’s lights to make sure they don’t drift too far from their boat.

“It’s all at the mercy of the current,” Hayes says. “You’re just moving with [the animals], lucky to encounter them.”