"Might be another machine room," she said, "but let's go. This track is terrible. If I wasn't made of iron I'd have bruises all over." He vaulted over the sill, reached down and hauled her after him. From behind them came the roar, sunk to a vague purring by the distance. They were in another granite-lined passage; one that went straight ahead for a few yards, then branched sharply. The right hand fork seemed to lead downward; automatically they took the other turn. A diffused radiance from somewhere high in the walls, as though the granite had been rendered transparent here and there, filled the whole place with shadowless light. For a time the passage ran level, then it climbed again, with another fork to the right, which dipped away from their level and which they again avoided. Of any other living being there was thus far no sign. The passage began climbing again, in a tight spiral, this time. "Good thing we're in training," remarked Marta Lami. "This is worse than the stairs in the Statue of Liberty." "Oh, did you fall for climbing that, too?" asked Sherman. "Sure. Publicity stunt about a year ago. Dumb bunny of a publicity man. Photographed on the old lady's spikes. Never will again." The spiral ended, a side passage branched off. The dancer stopped. "Sh," she said, "someone's coming. Duck in here." She seized Sherman's hand and led him into the side passage, down which they ran for a few feet, then paused to look back. Down the passage they had just vacated came a group of the ape-men, four or five of them, each carrying on his left arm a long, cylindrical shield like those one sees in pictures of Roman soldiers, and in his right hand some instrument that looked like a fire extinguisher with a long, flexible nozzle. Each of the group wore one of the helmets and behind them, wearing a similar headgear to which all the tubes were connected from the ape-men's helmets came one of the Lassans. The group hurried past without a sideward glance, the metal feet of the ape-men ringing oddly loud on the granite of the echoing passage. After a minute Sherman and the dancer crept cautiously forward; the procession had gone straight on down. Very likely a wrecking crew. Sherman and Marta sprinted up the passage in the direction from which the ape-men and their guide had come. The passage no longer rose with the same steepness, and as the ascent grew more gentle, the tunnel widened, with frequent side-passages to the right and branches leading down to the track at the left. Finally, after a sharp turn, it opened out into a big room, untenanted like all they had seen so far, filled with a complex maze of machinery, but machinery of a different character from that they had labored at. At the farther end of the room a door stood open. They dashed across it, plunged through--and found themselves in one of the enormous blue-domed halls, whose ceiling seemed to stretch miles above them. * * * * *