His altitude was still about five miles, and he was heading straight toward the huge, dark mass that soared in such geometrical perfection above the featureless plain. It was as blank as the flat white surface beneath; until now, he had not appreciated how enormous it really was. There were very few single buildings on Earth as large as this; his carefully measured photographs indicated a height of almost two thousand feet. And as far as could be judged, its proportions were precisely the same as TMA-l's – that curious ratio 1 to 4 to 9.

"I'm only three miles away now, holding altitude at four thousand feet. Still not a sign of activity – nothing on any of the instruments. The faces seem absolutely smooth and polished. Surely you'd expect some meteorite damage after all this time!

"And there's no debris on the – I suppose one could call it the roof. No sign of any opening, either. I'd been hoping there might be some way in.

"Now I'm right above it, hovering five hundred feet up. I don't want to waste any time, since Discovery will soon be out of range. I'm going to land. It's certainly solid enough – and if it isn't I'll blast off at once.

"Just a minute – that's odd -"

Bowman's voice died into the silence of utter bewilderment. He was not alarmed; he literally could not describe what he was seeing.

He had been hanging above a large, flat rectangle, eight hundred feet long and two hundred wide, made of something that looked as solid as rock. But now it seemed to be receding from him; it was exactly like one of those optical illusions, when a three-dimensional object can, by an effort of will, appear to turn inside out – its near and far sides suddenly interchanging.

That was happening to this huge, apparently solid structure. Impossibly, incredibly, it was no longer a monolith rearing high above a flat plain. What had seemed to be its roof had dropped away to infinite depths; for one dizzy moment, he seemed to be looking down into a vertical shaft – a rectangular duct which defied the laws of perspective, for its size did not decrease with distance...

The Eye of Japetus had blinked, as if to remove an irritating speck of dust. David Bowman had time for just one broken sentence which the waiting men in Mission Control, nine hundred million miles away and eighty minutes in the future, were never to forget:

"The thing's hollow – it goes on forever – and – oh my God! – it's full of stars!"

40 – Exit

The Star Gate opened. The Star Gate closed.

In a moment of time too short to be measured, Space turned and twisted upon itself.

Then Japetus was alone once more, as it had been for three million years – alone, except for a deserted but not yet derelict ship, sending back to its makers messages which they could neither believe nor understand.

VI – THROUGH THE STARGATE

41 – Grand Central

There was no sense of motion, but he was falling toward those impossible stars, shining there in the dark heart of a moon. No – that was not where they really were, he felt certain. He wished, now that it was far too late, that he had paid more attention to those theories of hyperspace, of transdimensional ducts. To David Bowman, they were theories no longer.

Perhaps that monolith on Japetus was hollow; perhaps the "roof" was only an illusion, or some kind of diaphragm that had opened to let him through. (But into what?) As far as he could trust his senses, he appeared to be dropping vertically down a huge rectangular shaft, several thousand feet deep. He was moving faster and faster – but the far end never changed its size, and remained always at the same distance from him.

Only the stars moved, at first so slowly that it was some time before he realized that they were escaping out of the frame that held them. But in a little while it was obvious that the star field was expanding, as if it was rushing toward him at an inconceivable speed.

The expansion was nonlinear; the stars at the center hardly seemed to move, while those toward the edge accelerated more and more swiftly, until they became streaks of light just before they vanished from view.

There were always others to replace them, flowing into the center of the field from an apparently inexhaustible source. Bowman wondered what would happen if a star came straight toward him; would it continue to expand until he plunged directly into the face of a sun? But not one came near enough to show a disk; eventually they all veered aside, and streaked over the edge of their rectangular frame.

And still the far end of the shaft came no closer. It was almost as if the walls were moving with him, carrying him to his unknown destination. Or perhaps he was really motionless, and space was moving past him...

Not only space, he suddenly realized, was involved in whatever was happening to him now. The clock on the pod's small instrument panel was also behaving strangely.

Normally, the numbers in the tenths-of-a-second window flickered past so quickly that it was almost impossible to read them; now they were appearing and disappearing at discrete intervals, and he could count them off one by one without difficulty. The seconds themselves were passing with incredible slowness, as if time itself were coming to a stop. At last, the tenth-of-a-second counter froze between 5 and 6.

Yet he could still think, and even observe, as the ebon walls flowed past at a speed that might have been anything between zero and a million times the velocity of light. Somehow, he was not in the least surprised, nor was he alarmed. On the contrary, he felt a sense of calm expectation, such as he had once known when the space medics had tested him with hallucinogenic drugs. The world around him was strange and wonderful, but there was nothing to fear. He had traveled these millions of miles in search of mystery; and now, it seemed, the mystery was coming to him.

The rectangle ahead was growing lighter. The hominous star streaks were paling against a milky sky, whose brilliance increased moment by moment. It seemed as if the space pod was heading toward a bank of cloud, uniformly Illuminated by the rays of an invisible sun.

He was emerging from the tunnel. The far end, which until now had remained at that same indeterminate distance, neither approaching nor receding, had suddenly started to obey the normal laws of perspective. It was coming closer, and steadily widening before him. At the same time, he felt that he was moving upward, and for a fleeting instant he wondered if he had fallen right through Japetus and was now ascending from the other side. But even before the space pod soared out into the open he knew that this place had nothing to do with Japetus, or with any world within the experience of man.

There was no atmosphere, for he could see all details unblurred, clear down to an incredibly remote and flat horizon. He must be above a world of enormous size – perhaps one much larger than Earth. Yet despite its extent, all the surface that Bowman could see was tessellated into obviously artificia1 patterns that must have been miles on a side. It was like the jigsaw puzzle of a giant that played with planets; and at the centers of many of those squares and triangles and polygons were gaping black shafts – twins of the chasm from which he had just emerged.

Yet the sky above was stranger – and, in its way, more disturbing – than even the improbable land beneath. For there were no stars; neither was there the blackness of space. There was only a softly glowing milkiness, that gave the impression of infinite distance. Bowman remembered a description he had once heard of the dreaded Antarctic "whiteout" – "like being inside a ping-pong ball." Those words could be applied perfectly to this weird place, but the explanation must be utterly different. This sky could be no meteorological effect of mist and snow; there was a perfect vacuum here.