Titan

ice began to form on the walls, and snow crunched underfoot. They do

"A thousand more steps?" Gaby suggested. "You must have read my mind."

The ice soon forced Cirocco to bend her head, then get on her hands and knees. It quickly grew dark again as Gaby led with the lamp in front of her. Cirocco paused and blew on her stiff hands, then got m her belly and crawled.

"Hey! I'm stuck!" She was pleased to hear no panic in her voice. It was frightening, but she knew she could get free if she backed up.

The scrabbling sounds in front of her stopped. "okay. I can't turn around here, but it's getting wider. I," go ahead and see what it's like. Twenty meters. Okay? "

"Right." She listened to the sounds getting farther away. The darkness closed in and she had just enough time to work up a very cold sweat before the light dazzled her. In a moment Gaby was back. There were ice crystals on her eyebrows.

"This is the worst spots right here." "Then I'll get through. I didn't come this far to end up like a cork in a bottle. "

"It's what you get for eating all those sweets, fatty." Gaby could not pull her through, so she backed up and man- aged to get the brass pick from her pack. They chipped, at the ice and tried it again.

"Breathe out," Gaby suggested. and tugged on her hands. She came through.

Behind them, a flat chunk of ice about a meter long fell from the roof and skidded noisily toward daylight.

"That must be why this passage is open," Gaby said. "The cable is flexible. It bends and the ice cracks."

"That and the warm air from behind us. Let's stop plugging it up, okay? Get moving."

Soon they could stand, and shortly afterward the ice was just a memory. They took off their coats and wondered what was next.

The rumbling began 400 steps farther on. It grew louder until it was easy to imagine huge machines thrumming just beyond the walls of the tu

They felt sure it was the sound of the air being sucked from the place of winds toward some unknown destination high above. Two thousand more steps brought them beyond it and into another hot region. They hurried through it, not bothering to strip as they knew they were close to the far end of the tu

Gaby was still in the lead, and saw the light first. it was no brighter than it had been on the other side, just a pale silver strip that began on their left and gradually widened until they were standing on a ledge beside the cable. They slapped each other on the back, then started climbing again.

They crossed over the top of the cable, always rising, always trending to the south, over the broad hump and down again on the far side. The cable was completely bare now; no trees, no earth clinging anywhere. It was the first time Gaea had really looked like the machine Cirocco knew it to be: the incredible, massive construct made by beings who might still be alive in the hub. The bare cable was smooth and straight, rising at an angle of sixty degrees now, getting closer to the flaring bottom edge of the spoke. The wedge of space between the cable and the spoke had narrowed to less than two kilometers.

On the south side the stairs entered another tu

"Damn! It's a different set-up. Let's go!"

"Which way?"

"Back would be just as bad as forward. Move!"

They would have been in danger only if one of them bad fallen and hurt herself, but it frightened Cirocco, and reminded her never to take Gaea for granted. She had forgotten the cable was made up of wound strands, and that the path of whatever hot and cold fluids ran through it could be quite complex.

They made it past the zone of vibration which was still in the center, and through the cold zone, which was not as choked with ice as the first had been, and emerged once again on the north side of the cable.

Across the top, and down into the third tu

They did that seven more times in two days. It would have been faster but for a delay in the fourth tu

But the next time they reached the south side of the cable,

there was no tu

Neither wanted to camp on a ledge a meter and a half wide that hung over a drop of 250 kilometers. Cirocco knew she tossed in her sleep and one toss could carry entirely too far. So, though both of them were weary, they kept trudging around and around the outside of the cable, always pressing their left shoulders to the reassuring solidity.

Cirocco did not like what was happening overhead. The nearer they got, the more impossible it looked.

They knew from their observations outside that each spoke was oval in cross-section, fifty kilometers thick one way and slightly less than a hundred the other, before it flared out to join the rim roof. They had just passed thuough that flaring section, and the spoke walls they could dimly see were nearly vertical. What they had not counted on was the lip that ran all the way around the monstrous bore of the spoke tube. It was easily five kilometers wide.

The cable seemed to enter the lip seamlessly, probably continuing above and traveling on to whatever tied it to the hub. During one of their rest stops they studied the lip, seemingly just above their heads, yet still two kilometers away. It was a massive ceiling to their labors, stretching endlessly until the opening became visible, narrowed by perspective. The opening was forty by eighty kilometers, but to reach it they would have to traverse five kilometers hanging from the underside of the lip.

Gaby looked at Cirocco and raised one eyebrow. "Don't borrow trouble. Gaea's been good to us so far. Climb, my friend."

And Gaea was good to them again. When they got to the top of the cable there was another tu

They lit the lamp, noting that there was not much fuel left, and began to climb. The tu

"It occurs to me," Gaby said, "that this could go all the way to the hub. And if you think that's good news, you'd better think against

"I know, I know. Keep climbing." Cirocco was thinking of lamp fuel, the state of their provisions, and the half-filled water- skins. It was still 300 kilometers to the hub. At three steps to the meter, that made it almost an even million steps yet to go. She looked at her watch and timed their pacing.

They had a rhythm of about two steps per second; just light touches of the toes to push them high enough to touch the next step. The gravity at that level had fallen to almost one eighth- half the already low gravity when they set out.

Two steps per second was half a million seconds of travel time. Eight three three three point three, etc., minutes, 138 hours, or nearly six days. Double that to include rest periods and sleep, at a conservative estimate ...

"I know what you're thinking," Gaby said, from behind her. "But can we do it in the dark?"

She had hit on the important point. The food could last two weeks. The water might be enough with rationing, but not for coming down.

But the crucial consumable at this stage was lamp fuel. They had no more than a five-hour supply, and no way to get more.

She was still working on it, trying to construct a mathematics that would get them to the top, when they emerged on the floor of the spoke.

Nothing had ever made Cirocco feel smaller. Not O'Neil One, not the stars in space, not the floor of Gaea herself. She could see everything, and her sense of perspective failed utterly.

It was impossible to detect the curvature of the walls. Like an upended horizon, they stretched away from her until suddenly they began to wrap around, making the space look more semi- circular than round.

Everything was bathed in a pale green luminescence. The source of the light was four vertical rows of windows which sent beams slanting down to cross each other in the empty center.

Not quite empty. Ru

Cirocco recalled thinking of the dark, narrow spaces beneath the cable they had explored as a cathedral. Gaea had exhausted her store of superlatives, but she knew that had only been an abandoned chapel. This was the cathedral.

"I thought I'd seen it all by now," Gaby said, quietly, pointing up at the wall behind them. "But a vertical jungle?"

There was no other way to describe it. Clinging to the walls, reaching outward or branching up, the inside of the spoke was crusted with more of the ubiquitous trees. They dwindled, becoming at some indeterminate distance just a smooth carpet of green. Beyond that was a gray roof.

"Would you say that's 300 kilometers up?"

Gaby squinted, then made a grid with her fingers and calculated with some system of her own.

"It covers the right number of degrees."

"Sit. Let's think on this."

She needed to sit more than she needed to think. Until this moment she had actually thought she could make it. She now saw that delusion had been fostered by an inability to visualize the problem. She could look at it now and she quailed inside. Three hundred kilometers, straight up.

Straight. Up.

She must have been insane.

"First. Does it look like there's any way through that roof?" Gaby looked, and shrugged.