The five hundredth rung seemed a good place to pause. He could feel the muscles in his arms responding to the unaccustomed exercise, even though Rama was now doing all the work and he had merely to guide himself.

“Everything OK, Skipper,” he reported. “We’re just passing the halfway mark. Joe, Will—any problems?”

“I’m fine—what are you stopping for?” Joe Calvert answered.

“Same here,” added Sergeant Myron. “But watch out for the Coriolis force. It’s starting to build up.”

So Mercer had already noticed. When he let go of the rungs he had a distinct tendency to drift off to the right. He knew perfectly well that this was merely the effect of Rama’s spin, but it seemed as if some mysterious force was gently pushing him away from the ladder.

Perhaps it was time to start going feet-first, now that “down” was beginning to have a physical meaning. He would run the risk of a momentary disorientation.

“Watch out—I’m going to swing round.”

Holding firmly on to the rung, he used his arms to twist himself round a hundred and eighty degrees, and found himself momentarily blinded by the lights of his companions. Far above them—and now it really was above—he could see a fainter glow along the rim of the sheer cliff. Silhouetted against it were the figures of Commander Norton and the back-up team, watching him intently. They seemed very small and far away, and he gave them a reassuring wave.

He released his grip, and let Rama’s still feeble pseudogravity take over. The drop from one rung to the next required more than two seconds; on Earth, in the same time, a man would have fallen thirty metres.

The rate of fall was so painfully slow that he hurried things up a trifle by pushing with his hands, gliding over spans of a dozen rungs at a time, and checking himself with his feet whenever he felt he was travelling too fast.

At rung seven hundred, he came to another halt and swung the beam of his helmet-lamp downwards; as he had calculated, the beginning of the stairway was only fifty metres below.

A few minutes later, they were on the first step. It was a strange experience, after months in space, to stand upright on a solid surface, and to feel it pressing against one’s feet. Their weight was still less than ten kilograms, but that was enough to give a feeling of stability. When he closed his eyes, Mercer could believe that he once more had a real world beneath him.

The ledge or platform from which the stairway descended was about ten metres wide, and curved upwards on each side until it disappeared into the darkness. Mercer knew that it formed a complete circle and that if he walked along it for five kilometres he would come right back to his starting point, having circumnavigated Rama.

At the fractional gravity that existed here, however, real walking was impossible; one could only bound along in giant strides. And therein lay danger.

The stairway that swooped down into the darkness, far below the range of their lights, would be deceptively easy to descend. But it would be essential to hold on to the tall handrail that flanked it on either side; too bold a step might send an incautious traveller arching far out into space. He would hit the surface again perhaps a hundred metres lower down; the impact would be harmless, but its consequences might not be—for the spin of Rama would have moved the stairway off to the left. And so a falling body would hit against the smooth curve that swept in an unbroken arc to the plain almost seven kilometres below.

That, Mercer told himself, would be a hell of a toboggan ride; the terminal speed, even in this gravity, could be several hundred kilometres an hour. Perhaps it would be possible to apply enough friction to check such a headlong descent; if so, this might even be the most convenient way to reach the inner surface of Rama. But some very cautious experimenting would be necessary first.

“Skipper,” reported Mercer, “there were no problems getting down the ladder. If you agree, I’d like to continue towards the next platform. I want to time our rate of descent on the stairway.”

Norton replied without hesitation.

“Go ahead.” He did not need to add, “Proceed with caution.”

It did not take Mercer long to make a fundamental discovery. It was impossible, at least at this one-twentieth-of-a-gravity level, to walk down the stairway in the normal manner. Any attempt to do so resulted in a slow-motion dreamlike movement that was intolerably tedious; the only practical way was to ignore the steps, and to use the handrail to pull oneself downwards.

Calvert had come to the same conclusion.

“This stairway was built to walk up, not down!” he exclaimed. “You can use the steps when you’re moving against gravity, but they’re just a nuisance in this direction. It may not be dignified, but I think the best way down is to slide along the handrail.”

“That’s ridiculous,” protested Sergeant Myron. “I can’t believe the Ramans did it this way.”

“I doubt if they ever used this stairway—it’s obviously only for emergencies. They must have had some mechanical transport system to get up here. A funicular perhaps. That would explain those long slots running down from the Hub.”

“I always assumed they were drains but I suppose they could be both. I wonder if it ever rained here?”

“Probably,” said Mercer. “But I think Joe is right, and to hell with dignity. Here we go.” The handrail—presumably it was designed for something like hands—was a smooth, flat metal bar supported on widely-spaced pillars a metre high. Commander Mercer straddled it, carefully gauged the braking power he could exert with his hands, and let himself slide. Very sedately, slowly picking up speed, he descended into the darkness, moving in the pool of light from his helmet-lamp. He had gone about fifty metres when he called the others to join him. None would admit it, but they all felt like boys again sliding down the banisters. In less than two minutes, they had made a kilometre descent in safety and comfort. Whenever they felt they were going too fast a tightened grip on the handrail provided all the braking that was necessary.

“I hope you enjoyed yourselves,” Commander Norton called when they stepped off at the second platform. “Climbing back won’t be quite so easy.”

“That’s what I want to check,” replied Mercer, who was walking experimentally back and forth, getting the feel of the increased gravity. “It’s already a tenth of a gee here—you really notice the difference.”

He walked—or, more accurately, glided—to the edge of the platform, and shone his helmet-light down the next section of the stairway. As far as his beam could reach, it appeared identical with the one above—though careful examination of photos had shown that the height of the steps steadily decreased with the rising gravity. The stair had apparently been designed so that the effort required to climb it was more or less constant at every point in its long curving sweep.

Mercer glanced up towards the Hub of Rama, now almost two kilometres above him. The little glow of light, and the tiny figures silhouetted against it, seemed horribly far away. For the first time, he was suddenly glad that he could not see the whole length of this enormous stairway. Despite his steady nerves and lack of imagination, he was not sure how he would react if he could see himself like an insect crawling up the face of a vertical saucer more than sixteen kilometres high—and with the upper half overhanging above him. Until this moment, he had regarded the darkness as a nuisance; now he almost welcomed it.

“There’s no change of temperature,” he reported to Commander Norton. “Still just below freezing. But the air pressure is up, as we expected—around three hundred millibars. Even with this low oxygen content, it’s almost breathable; further down there will be no problems at all. That will simplify exploration enormously. What a find—the first world on which we can walk without breathing gear! In fact, I’m going to take a sniff.”