Sandy said thoughtfully, "If men had built this, there'd be signs somewhere marking things. At least there'd be some sort of numbers on these doorways!" Burke said nothing. They went on. The gallery branched. A metal door closed off the divergent branch. Burke tugged at an apparent handle. It did not yield. They continued along the straight, open way. They came to a larger-than-usual opening in the side wall. Inside it there were rows and rows and rows of metal spheres some ten feet in diameter. There must have been hundreds of them. Beside the door there was a tiny shelf, with a tinier box fastened to it. A long way farther, they came to what had appeared to be the end of this corridor. But it did not end. It slanted upward and turned and they found themselves in the same corridor on a different level, headed back in the direction from which they had come. Their footsteps echoed hollowly in the still-enormous emptiness. There were other closed doors. Burke tried some. Holmes tried others. They did not open. Keller moved raptly, gazing at this and that. Everything was strange, but not strange enough to be frightening. One could have believed this place the work of men, except that this was beyond the ability of men to make. There must be miles of vacant rooms carved out of solid rock. They came upon some hundreds of yards of doorways, and in every room on which they opened, there were metal frames about the walls. Holmes said suddenly, "If men had built this place, those could be bunks." They came to another place where there was dust, and a group of six huge rooms communicating not only with the corridor but with each other. They found hollow metal things like cook pans. They found a hollow small object which could have been a drinking vessel. It was broken. It was of a size suitable for men. "If men built this," said Holmes again, "these could be mess-halls. But I agree with Sandy that there should be signs." Yet another closed door. It resisted their efforts to open it, just like the others. Keller put out his hand and thoughtfully touched the stone beside it. He looked astonished. "What?" asked Burke. He touched the stone as Keller had. It was bitterly, bitterly cold. "The air's warm and the stone's cold! What's this?" Keller wetted the tip of his finger and rubbed it on the rocky side wall. Instantly, frost appeared. But the air remained warm. The gallery turned again, and again rose. The third-level passageway was shorter; barely half a mile in length. Here they passed door after door, all open, with each compartment containing a huge and somehow malevolent shape of metal. And beside each doorway there was a little shelf with a small box fastened to it. "These," said Holmes, "could be guns, if there were any way for them to shoot anything. Just by the look of them I'd say they were weapons."