There were hundreds if not thousands of honeycombed entrances and he had chosen one pretty much at random. All of them were large enough to drive a truck into, or nearly, and one seemed as good as another for a cursory investigation within. Using the footpads inside the hardsuit, he activated the vertical thrust until he was up about twenty feet and at eye-level with the opening he wanted. Murphy hovered just behind him. Exterior suit lights cast a pool of illumination around him. He would not use his spots until he found something worthy of closer examination.

A slight tap of the horizontal thrusters and he entered the mouth of the tunnel that led into the belly of the city. It was perfectly circular, though it did not seem so with all the clustered growths of corals and carbonate skeletons of dead marine animals clinging to the walls like lumpy stucco. Green, slimy weeds grew up from the floor, swaying with a dreamlike motion from currents deep within. The suit halogens cast a swath of light for about twelve feet in front of him, but beyond that was an utter, colossal blackness. Clots of sediment slowly drifted about.

Ten feet in, he felt waves of anxiety wash through him. Looking at the city from outside was bad enough, but entering it unnerved him, made him feel somehow unclean. It was like sliding into the carcass of something long dead.

The weeds brushed against his suit with a dull rustling sound. The suit’s sonar told him that the tunnel went on for about sixty feet. The water temperature was 38° Fahrenheit.  There was a light current coming from ahead. Nothing in the tunnel, said the sonar, but themselves. Thirty feet into it, side passages opened up. Others went through the floor and still others through the ceiling. A labyrinth.

Murphy did not suggest going into them, but over the radio Bell said, “We stay on a straight course, make for that opening ahead.”

“Roger that,” Murphy said.

“What kind of magnetism we getting?”

Murphy had the magnetometer hooked to his suit. “Ah…holding steady at about one-ten. No increase yet.”

Bell nodded inside his helmet. Something which was ridiculous since no one could see him. But like facial expressions, it was nearly impossible to get out of the habit.

Magnetism was measured in nanoteslas. About 70,000 nT was average at Kharkov Station. But the anomaly routinely put out sometimes four or five times that amount. When it started going off the scale, they would be in the vicinity of the anomaly itself.