A horizontal slab protruded like a Stone Age awning from the rock face near the platform. Beneath the slab was a rectangular opening the size and shape of a doorway. Drifting closer, Nina squinted through her face mask lens and tried to pierce the menacing blackness. She remembered her headlamp and switched it on. The shaft of light fell on a whirl of ghostly movement. She drew back in alarm. Then a laugh bubbled from her regulator The silverscaled school of fish that had made the tunnel its home was more startled than she was.

As her pulse returned to normal she recalled Dr. Knox’s warning: Don’t risk your neck for a nugget of knowledge that would end up in a dusty tome read by a few. With fiendish delight he’d relate in grim detail the fates of scientists who went too far. Furbush was devoured by cannibals. Rozzini was consumed by malaria. ONeil dropped into a bottomless crevasse.

Nina was convinced Knox made the names up, but she took his point. She was alone, without a lifeline to unreel behind her. Nobody knew where she was. The very element of danger that should have repelled her was seductive in its appeal. She checked her pressure gauge. By snorkeling, she’d used her. air supply sparingly and still had time left.

She made a pact with herself to stop just inside the opening and go no farther. The tunnel couldn’t be very long. Primitive tools, not diamond drills, had been used to cut through the rock. She shot some pictures of the entrance, then moved forward.

Incredible!

The floor was almost perfectly flat, the walls smooth except for shaggy marine growth.

She went in deeper, forgetting her pact and Knox’s sage advice as well. The tunnel was the most beautiful artifact she had ever seen. It was already longer than a similar passageway at the submerged city of Apollonia.

The smooth sides ended abruptly, becoming a roughsided cave that narrowed and widened, meandering in more or less of a straight line, with smaller passages branching off. Sconces for lamps were set into the carbonblackened walls. The tunnel borers had extended the natural cave by making an artificial one. Nina marveled at the skill and determination of long dead Bronze Age sandhogs.

The passageway once again became wider and more polished. Nina squeezed over the top of a pile of rubble, encouraged by a greenish glow in the distance. She swam to the light, which became brighter the nearer she came.

In pursuit of knowledge Nina had crawled through piles of bat guano and lairs guarded by badtempered scorpions. As wondrous as the tunnel was, she was anxious to be out of it and drew a sigh of relief when the passage ended. She floated up a stairway and through an archway, emerging into an open space surrounded by crumbled foundations.