As he went lower he heard a humming sound that grew louder while he descended. At the bottom he came out in a damp tunnel that had a trickle of water down the middle, and the hum was now a hammering roar that filled the shaft with sound. Chimal went forward carefully, alert for any motion, until the tunnel ended in a high cavern that held towering metal objects from which the torrent of sound poured. He had no idea what their function might be. Great round sections of them vanished up into the stone above, and from one of these sections came the dribble of water that ran across the floor and into this tunnel. From the security of the entrance he ran his eye down the row of immense things, to the far end where brighter lights shone on a board of smaller shining objects before which a man sat. Chimal drew back into the tunnel. The man’s back was to him and he had certainly not seen the intruder yet. Chimal went back down the tunnel and past the metal stairs. He would see where this led before he went back to the chamber of cars.

As he walked the noise behind him lessened and, when it had died away to a distant hum, he was aware of the sound of running water coming from somewhere ahead. Darkness filled the mouth of the tunnel. He stepped through it onto a ledge above the blackness. A row of lights, curving away to his left, reflected from a dark surface. He realized that he was looking at a vast underground lake: the running water sounded far out ahead of him and small waves trembled the reflections on the surface. The cavern that held the water was vast and the echoes of the falling water sounded on all sides. Where was this place? In his mind he ran through the turnings he had made, and tried to estimate how far he had come. He was much lower than when he had started, and had come north, and then east Looking up he could imagine his route — and there above would be the swamp at the north end of the valley. Of course! This underground lake lay beneath the swamp and drained it. The things back there in the cavern did something to force the water through pipes back to the waterfall. And where did the row of lights go that skirted the edge of the dark lake? He walked forward to find out

A ledge had been cut from the rock of the cavern wall and the lights were spaced along it The rock was slippery and damp and he went carefully. One quarter of the way around the water it went, then ended at another tunnel. Chimal realized that he was tired. Should he go on, or return to his hiding place? That would be the wisest thing to do, but the mystery of these caverns drew him forward. Where did this one lead? He started into it. It was damp, mustier than the other tunnels, though it was lit by the same evenly spaced windows of light No, not as even as the others, a black gap showed ahead like a missing tooth. When he came up to this spot he saw that one of the smooth objects was inset there — but this one’s fire was gone and it was dark. The first one he had seen like this. Perhaps this tunnel was rarely used and this had not been noticed yet. At the end of the tunnel was another round stairway of metal up which he climbed. This emerged into a small room that had a door in one wall. When he put his ear to the door he heard nothing from the other side. He opened it a narrow crack and looked through.

This cavern was quiet, empty, and the largest one he had yet encountered. When he entered it the sound of his footsteps made a tiny rustle in its towering vastness. The lighting here was far less than that of the tunnels, but it was more than enough to show him the size of this cavern, and the paintings that adorned the walls. These were lifelike and strange, people and unusual animals and even odder metal objects. They were marching, all of them, a torrent of frozen motion, going toward the far end of the cavern where there was a doorway flanked by golden statues. The people of the paintings were dressed in different and fantastic Ways, and were even of different skin colors, but they all went to a common goal. The pressure of these silent marchers drove him that way too, but not before he looked about him.

The other end of the cavern was sealed with immense boulders that, for some reason, looked familiar to him. Why? He had never been in this place before. He walked closer to them and looked up at their piled magnitude. They reminded him very much of the rock barrier that sealed the end of the valley.

Of course! This was the other side of that same barrier. If the gigantic boulders were removed the valley would be open, and he did not doubt for a second that the powers that had been used to carve these tunnels and build a sun could be used to throw aside the rocks in front of him. From outside there had appeared to be no exit from the valley — because the exit was sealed inside the rock. Could the legends be true? That some day the valley would be open and his people would march forth. To where? Chimal spun about and looked at the high opening at the far end of the chamber. What did it lead to?

He passed between the large, golden statues of a man and a woman that flanked the portal, and then continued down the tunnel beyond. It was wide and straight and patterned with gold designs. Many doors opened off it but he did not examine any of them: that would wait They doubtless contained many things of interest, but they were not the reason for this passageway. That lay ahead. Faster and faster he walked until he was almost running, up to the great double doors of gold that sealed the end. There was only silence behind them. There was a strange tautness in his chest as he pushed them open.

Beyond was a large chamber, almost as big as the other one, but this one was undecorated and dark, with just a few small lights to show him the way. There was a rear wall and sides, but the far wall was missing. The opening faced out on the star-filled night sky.

It was no sky that Chimal had ever seen before. There was no moon in sight and no valley walls to form a close horizon. And the stars, the stars, the overwhelming quantity of them that broke over him like a wave! The familiar constellations, if they were there, were lost in the infinity of the other stars as numberless as grains of sand. And aft of the stars were turning, as though mounted on a great wheel. Some faint, tiny; others blazing like torches of many colors, yet they all were hard and clear points of light without lie flickering of the stars above his valley.

What could this mean? In uncomprehending awe he walked forward until he collided with something cold and invisible. The sudden spurt of fear dissipated as he touched it with his hand and realized it must be the same kind of transparent substance that covered the front of the cars. Then this entire wall of the room was a great window, opening out on — what? The window curved outward and when he leaned into it he could see that the stars filled the sky to left and right, above and below. He had a sudden vertigo, as though he were falling and pressed his hand to the window, but the unaccustomed cold of it was strangely ominous and he quickly pulled away. Was this another valley facing the real universe of stars? If so, where was the valley?

Chimal stepped back, unsure, frightened by this new immensity, and as he did he heard a faint sound.

Was it a footstep? He started to jump about when the killing thing was suddenly jerked from his hand. He fell back against the cold window and saw the Master Observer and three other men standing before him, all of them pointing the deadly flame weapon at him.

“You have come at last to the end,” the Master Observer said.