"You could also use the ring for takeoff."

"No. Observe the facility to our left."

"I'll be tanjed," said Louis Wu.

The "facility" was little more than a trap door big enough to hold one of the ramships.

It figured. 770 miles per second was ramscoop speed. The rines launching facility was merely a structure for tumbling the ship off into the void. The pilot would immediately accelerate away on ramscoop-fumon power.

"The spaceport facility seems to be abandoned," said Speaker.

"Is there power in use?"

"My instruments sense none. There are no anomolous hot spots, no large-scale electromagnetic activities. As for the sensors which operate the linear accelerator, they may use less power than we can sense."

"Your suggestion?"

"The facilities may still be in operational condition. We can test this by proceeding to the mouth of the linear accelerator and entering."

Nessus curled himself into a ball.

"Wouldn't work," said Louis. "There could be a key signal to start the thing, and we don't know it. It might react only to a metal hull. If we tried to go through the cannon at the speed of the Ringworld, we'd hit one of the coils and blow everything to bits."

"I have flown ships under similar conditions during simulated war maneuvers."

"How long ago?"

"Perhaps too long. Never mind. Your suggestion?"

"The underside," said Louis. The puppeteer uncurled at once.

They hovered beneath the Ringworld floor, matching velocities, thrusting outward at 9.94 meters per second. "Spotlights," said Nessus.

The spots reached across half a thousand miles; but if their light touched the back of the ring, it did not return. The spots were for landings.

"Do you still trust your engineers, Nessus?"

"They should have anticipated this contingency."

"But I did. I can light the Ringworld, if I may use the fusion drives," said the kzin.

"Do so."

Speaker used all four: the pair facing forward, and the larger motors facing back. But on the forward pair, the pair intended for emergency braking and possibly for weapons, Speaker choked the nozzle wide open. Hydrogen flowed though the tube too fast, emerged half-burnt. Fusion-tube temperature dropped until the exhaust, usually hotter than the core of a nova, was as cool as the surface of a yellow dwarf star. Light thrust forward in twin spears to fall across the black underside of the Ringworld.

First: the underside was not flat. It dipped and rose; there were bulges and indentations.

"I thought it would be smooth," said Teela.

"Sculptured," said Louis. "I'll make you a bet. Whereever we see a bulge, there's a sea on the sunlit side. Where we see a dent, there's a mountain."

But the formations were tiny, unnoticeable until Speaker drew the ship close. The Lying Bastard drifted in from the Ringworld's edge, half a thousand miles beneath her underbelly. Sculptured bulges and sculptured indentations, they drifted by, irregular, somehow pleasing …

For many centuries excusion boats had drifted in like manner across the surface of Earth's Moon. The effect here was much the same: airless pits and peaks, sharp-edged blacks and whites, exposed on the Moon's dark side by the powerful spotlights carried by all such boats.

Yet there was a difference. At any height above the Moon, you could always see the lunar horizon, sharp and toothy against black space and gently curved.

There were no teeth in the Ringworld's horizon, and no curves. It was a straight line, a geometer's line, unimaginably distant; barely visible as black-against-black. How could Speaker stand it? Louis wondered. Hour after hour, driving the Liar across and beneath the belly of this … artifact.

Louis shuddered. Gradually he was learning the size, the scale of the Ringworld. It was unpleasant, like all learning processes.

He drew his eyes away from that terrible horizon, back to the illuminated area below/above them.

Nessus said, "All the seas seem to be of the same order of magnitude."

"I've seen a few ponds," Teela contradicted him. "And look, there's a river. It has to be a river. But I haven't seen any big oceans."

Seas there were in plenty, Louis saw — if he was right, and those flat bulges were seas. Though they were not all the same size, they seemed evenly distributed, so that no region was without water. And — "Flat. All the seas have flattened bottoms."

"Yes," said Nessus.

"That proves it. All the seas are shallow. The Ringworlders aren't sea-dwellers. They use only the top of an ocean. Like us."

"But all the seas have squiggly shapes," said Teela. "And the edges are always ragged. You know what that means?"

"Bays. All the bays anyone can use."

"Though your Ringworlders are land-dwellers, they do not fear boats," said Nessus. "Else they would not need the bays. Louis, these people will resemble humans in outlook. Kzinti hate water, and my species fears to drown."

You can learn a lot about a world, Louis thought, by looking at its underside. Someday he would write a monograph on the subject …

Teela said, "It must be nice to carve your world to order."

"Don't you like your world, playmate?"

"You know what I mean."

"Power?" Louis liked surprises; he was indifferent to power. He was not creative; he did not make things; he preferred to find them.

He saw something ahead of them. A deeper bulge … and a projecting fin, black in the light of the throttled drives, hundreds of thousands of square miles in area.

It the others were seas, this was an ocean, the king of all oceans. It went by them endlessly; and its underbelly was not flat. It looked like a topographical map of the Pacific Ocean: valleys and ridges, shallows and depths and peaks tall enough to be islands.

"They wanted to keep their sea life," Teela guessed. "They needed one deep occan. The fin must be to keep the depths cool. A radiator."

An ocean not deep enough, but easily broad enough, to swallow the Earth.

"Enough of this," the kzin said suddenly. "Now we must see the inner surface."

"First then are measurements to take. Is the ring truly circular? A minor deviation would spill the air into space."

"We know that there is air, Nessus. The distribution of water on the inner surface will tell us how the ring deviates from circularity."

Nessus surrendered. "Very well. As soon as we reach the further rim."

There were meteor wormholes. Not many, but they were there. Louis thought with amusement that the Ringworlders had been remiss in cleaning out their solar system. But no, these must have come from outside, from between the stars. One conical crater floated by in the fusion light and Louis saw a glint of light at the bottom. something shiny, reflecting.

It must be a glimpse of the ring floor. The ring floor, a substance dense enough to stop 40 percent of neutrinos, and presumably very rigid. Above/inward from the ring floor, soil and seas and cities, and above these, air. Below/outward from the ring floor, a spongy material, like foam plastic perhaps, to take the brunt of a meteoroid impact. Most meteoroids would vaporise within the thick foamed material; but a few would get through, to leave conical holes with shiny bottoms …

Far down the length of the Ringworld, almost beyond its infinitely gentle curve, Louis's eyes found a dimple. That must have been a big one, he thought. Big enough to show by starlight, that far away.

He did not call attention to the meteoroid dimple. His eyes and mind were not yet used to the proportions of the Ringworld.