This area of the city was almost deserted. Although the population of Diaspar had not altered for millennia, it was the custom for families to move at frequent intervals. One day the tide of life would sweep this way again, but the great towers had been lonely now for a hundred thousand years.

             The marble platform ended against a wall pierced with brilliantly lighted tunnels. Alvin selected one without hesitation and stepped into it. The peristaltic field seized him at once, and propelled him forward while he lay back luxuriously, watching his surroundings.

             It no longer seemed possible that he was in a tunnel far underground, the art that had used all Diaspar for its canvas had been busy here, and above Alvin the skies seemed open to the winds of heaven. All around were the spires of the city, gleaming in the sunlight. It was not the city as he knew it, but the Diaspar of a much earlier age. Although most of the great buildings were familiar, there were subtle differences that added to the interest of the scene. Alvin wished he could linger, but he had never found any way of retarding his progress through the tunnel.

             All too soon he was gently set down in a large elliptical chamber, completely surrounded by windows. Through these he could catch tantalizing glimpses of gardens ablaze with brilliant flowers. There were gardens still in Diaspar, but these had existed only in the mind of the artist who conceived them. Certainly there were no such flowers as these in the world today.

             Alvin stepped through one of the windows—and the illusion was shattered. He was in a circular passageway curving steeply upward. Beneath his feet the floor began to creep slowly forward, as if eager to lead him to his goal. He walked a few paces until his speed was so great that further effort would be wasted.

             The corridor still inclined upward, and in a few hundred feet had curved through a complete right angle. But only logic knew this: to the senses it was now as if one were being hurried along an absolutely level corridor. The fact that he was in reality traveling up a vertical shaft thousands of feet deep gave Alvin no sense of insecurity, for a failure of the polarizing field was unthinkable.

             Presently the corridor began to slope "downward" again until once more it had turned through a right angle. The movement of the floor slowed imperceptibly until it came to rest at the end of a long hall lined with mirrors. Alvin was now, he knew, almost at the summit of the Tower of Loranne.

             He lingered for a while in the hall of mirrors, for it had a fascination that was unique. There was nothing like it, as far as Alvin knew, in the rest of Diaspar. Through some whim of the artist, only a few of the mirrors reflected the scene as it really was—and even those, Alvin was convinced, were constantly changing their position. The rest certainly reflected something, but it was faintly disconcerting to see oneself walking amid ever-changing and quite imaginary surroundings. Alvin wondered what he would do if he saw anyone else approaching him in the mirror-world, but so far the situation had never arisen.

             Five minutes later he was in a small, bare room through which a warm wind blew continually. It was part of the tower's ventilating system, and the moving air escaped through a series of wide openings that pierced the wall of the building. Through them one could get a glimpse of the world beyond Diaspar.

             It was perhaps too much to say that Diaspar had been deliberately built so that its inhabitants could see nothing of the outer world. Yet it was strange that from nowhere else in the city, as far as Alvin knew, could one see the desert. The outermost towers of Diaspar formed a wall around the city, turning their backs upon the hostile world beyond, and Alvin thought again of his people's strange reluctance to speak or even to think of anything outside their little universe.

             Thousands of feet below, the sunlight was taking leave of the desert. The almost horizontal rays made a pattern of light against the eastern wall of the little room, and Alvin's own shadow loomed enormous behind him. He shaded his eyes against the glare and peered down at the land upon which no man had walked for unknown ages.

             There was little to see: only the long shadows of the sand dunes and, far to the west, the low range of broken hills beyond which the sun was setting. It was strange to think that of all the millions of living men, he alone had seen this sight.

             There was no twilight: with the going of the sun, night swept like a wind across the desert, scattering the stars before it. High in the south burned a strange formation that had puzzled Alvin before—a perfect circle of six colored stars, with a single white giant at its center. Few other stars had such brilliance, for the great suns that had once burned so fiercely in the glory of youth were now guttering to their doom.

             For a long time Alvin knelt at the opening, watching the stars fall toward the west. Here in the glimmering darkness, high above the city, his mind seemed to be working with a supernormal clarity. There were still tremendous gaps in his knowledge, but slowly the problem of Diaspar was beginning to reveal itself.

             The human race had changed—and he had not. Once, the curiosity and the desire for knowledge which cut him off from the rest of his people had been shared by all the world. Far back in time, millions of years ago, something must have happened that had changed mankind completely. Those unexplained references to the Invaders—did the answer lie there?

             It was time he returned. As he rose to leave, Alvin was suddenly struck by a thought that had never occurred to him before. The air vent was almost horizontal, and perhaps a dozen feet long. He had always imagined that it ended in the sheer wall of the tower, but this was a pure assumption. There were, he realized now, several other possibilities. Indeed, it was more than likely that there would be a ledge of some kind beneath the opening, if only for reasons of safety. It was too late to do any exploring now, but tomorrow he would come again. . . .

             He was sorry to have to lie to Jeserac, but if the old man disapproved of his eccentricities it was only kindness to conceal the truth. Exactly what he hoped to discover, Alvin could not have said. He knew perfectly well that if by any means he succeeded in leaving Diaspar, he would soon have to return. But the schoolboy excitement of a possible adventure was its own justification.

             It was not difficult to work his way along the tunnel, though he could not have done it easily a year before. The thought of a sheer five-thousand-foot drop at the end worried Alvin not at all, for Man had completely lost his fear of heights. And, in fact, the drop was only a matter of a yard onto a wide terrace running right and left athwart the face of the tower.

             Alvin scrambled out into the open, the blood pounding in his veins. Before him, no longer framed in a narrow rectangle of stone, lay the whole expanse of the desert. Above, the face of the tower still soared hundreds of feet into the sky. The neighboring buildings stretched away to north and south, an avenue of titans. The Tower of Loranne, Alvin noted with interest, was not the only one with air vents opening toward the desert. For a moment he stood drinking in the tremendous landscape: then he began to examine the ledge on which he was standing.

             It was perhaps twenty feet wide, and ended abruptly in a sheer drop to the ground. Alvin, gazing fearlessly over the edge of the precipice, judged that the desert was at least a mile below. There was no hope in that direction.