Diver Finds Structure on Ocean Floor — Then Finds Out Why It’s There

A hole in the floor

He floated slowly through the narrow chamber, circling the area methodically, the beam of his flashlight sweeping the interior. Then he spotted it—a hole in the floor, perfectly circular, about a meter across. He hovered above it, peering down into the shaft below. Without hesitation, he adjusted his gear, angled himself feet-first, and dropped into the vertical tunnel.