"What happened to us is absurd," Lidal Kelner said. "While the structure we're trapped on is logically possible, there's no reason for it to exist. Logic is useless here. We might as well rely on intuition."
   Ella Komptris and Thurys Han studied their commander. They were crowded in the small Bridge. Anticipation had been building for weeks.
   Valmar Rogers sat in the control seat, wrapped in a Reality Blanket.
   "I think it's a test," Ella said. "This week we've come 1335 kilometers closer to the end." The ship's navigator enthusiastically tracked their progress.
   The Bridge vibrated slightly as the converted starship Mordos passed over a boulder field. It was crossing an almost literally endless plain that seemed Earth-like at first glance. The brown grass looked dead, but a rich ecosystem thrived under the blades. Straight tracks formed perpendicular to their course as creatures fled the passing ship. Telescopic necks popped up and retracted.
   Valmar concentrated on the sunlit landscape filling his vision. He experienced their surroundings almost directly. The steady airflow, the barely visible high horizon, and the long wave Mordos made in the prairie were his only link with Outside. He enjoyed the sensations, forgetting they were trapped inside their sterile crypt until their return to Earth.
   For now, the beauty of the landscape was enough. It had taken Valmar years to notice all the hidden patterns. For example, those low hills in the middle distance lined up with the valley they had just crossed.
Branching and curving in all directions, the rivers most definitely did not take the shortest routes to the seas, which in turn had unusually jagged shores with far too many islands.
A world designed to maximize evolution. He was convinced its geography could be described by a complex fractal equation.
   Valmar listened to the ongoing argument over the engine roar. Their micro society was slowly perfecting itself. He loved to explore; Ella's obsession with the optimal course came from a programmed desire to return home (which would vanish the moment they did get back); while Thurys's resource-mapping was a shareholder-inserted greed compulsion. Lidal was balanced between caution and brilliance.
   The ground-effect plate of their converted starship raised a cloud of dust. On top were retractable legs and wheels for rough terrain, when air pressure wasn't enough.
He checked the view from different points on the hull, small particles seemingly stinging his eyes. The vibration didn't affect him. Looking up along the ship's flank, he was briefly blinded by the sunlight. The illusion was convincing, but there was no sun in the alien sky. Instead, a thin strip of light hung there, narrowing and tapering out in the distance.
   He listened while Lidal stated his evolving beliefs.
   "We are intruders." He wanted to put the crew in static hibernation until aliens found them. They might know a way out of Hoverworld.
The centuries had changed them. Physically, they still appeared to be in their early thirties, but they were different people than when they had landed. "The magic carpet effect," Valmar had said.
   In the coming weeks they would learn more. Despite occasional monotony, no two days were alike. Wheeled animals, living clouds, missile trees and far stranger things could be found in some valleys.
Valmar stared at the forward horizon, which seemed to be shimmering. He hoped it wasn't a mirage.
   "The Wall is in sight," he finally said. A moment of silence, then cheering.
   Ascent Week was here. They had enacted this ritual many times over.
Their inability to lose hope or give up was a side effect of the life extension therapy. Old memories were constantly recompressed, the accumulating wonders crowding each other out.
It helped them to adapt. They literally couldn't stay the same person for longer than a few years.
   For a moment, Valmar forgot what subjective year it was. Everything was stored in the ship's log, and key events remained indelible. He remembered their arrival on Hoverworld, impossible ages ago.

   Their five-man starship Mordos, the most complex object mankind could construct, had an inherent limit. Every jump through Superspace was a leap into the unknown. When they arrived in some incalculably distant new galaxy, the scene usually looked familiar enough: they saw the typical distribution of stars and quasars, and the lumpiness of the microwave background was just about right - but it was invariably a place no human had ever visited before.
Without recognizable landmarks, they couldn't know how far they had traveled. In fact the distance from Earth might as well be infinite.
   It was always possible to return to their starting point, and to repeat any trip at a later date. After countless random jumps, an exploration vessel would eventually emerge within range of an alien radio beacon, and proceed to make contact. The ships' fusion scoops and life extension systems gave them transgalactic ranges.
   Humanity had many new worlds to discover. Like other empires, it was spread evenly throughout the universe. So far, contact had been established with 83 alien species. Many more had no doubt been overlooked. "Slow travelers" connected the arrival points of different species.
   This was the first chapter of the Great Game. Someday every atom, every cubic lightyear of space, would be claimed by someone. The objective was to grab as much territory as possible as early as possible - a dangerous opportunity.
   Their training at SpaceCom's elite Cantor University had been an intense indoctrination. While the students enjoyed all the luxuries of TransHumanity, their courses emphasized extreme danger. If a starship hull's inner seal was broken, it would no longer match its quantum twin on Earth, and it could never return home. No conceivable technology could defeat this simple precaution.
The only threat was the information contained in the minds of the travelers. They would be quarantined immediately upon their return.
   Return to Earth . . . the foundation of their universe.
   Only a few ships had ever been lost. Who could have anticipated Hoverworld?

   They had no right to be surprised, Valmar pointed out. Humanity was humbled by the works of many older species, who had transformed entire solar systems and converted nebulae into energy. Thousands of star modifications and extensions had been spotted from great distances.
   The most advanced civilizations disassembled their suns. First, they sped up the star's rotation, flattening it into a disk. The glowing remnants broke into concentric rings that were harvested in turn. Diskworlds extended for tens of billions of kilometers.
   What happened next was less clear. Great latticeworks hung in the void, scattering the light of more distant stars. Larger structures didn't even use centrifugal force to generate the effects of gravity, but relied on their own mass. The largest used rotation to counteract it.
   Progress never ended. There were strange galaxies at the limits of visual range, patterns of background radiation that seemed too regular. Contacting these anomalies was prohibited, and probably impossible anyway.

   "You remember the reports from Orf," Ella said. "From the outside it looked like an ordinary star. That was weirder than this place."
   Valmar nodded sagely. Over the years he had postulated many strange supercivilizations. "A deep gravity well could be expanded from within, using negative energy," he pondered. "Its inhabitants would be repelled from the core singularity."
   "This place is stranger than that," Lidal insisted.

   When they had first approached Hoverworld, there had been no time to react. The alarms went off as Mordos was pulled into a glowing haze at relativistic speeds. If they ever made it back, Lidal would claim the matter beam had resembled a beacon. That wasn't quite true. Space Command discouraged exploration for its own sake. Unexplained anomalies were to be avoided.
   Within seconds they had been caught, dragged inexorably along an invisible corridor in space. Electricity crackled over the hull as the outer coating was worn away.
   The beam decelerated as it widened, and they rode the turbulence to its edge.
Ahead loomed a pale green-blue planet that at first glance resembled Uranus, albeit hundreds of times wider, with a thin line around the equator. Illumination was constant across its surface. Looking closer, they saw an endless mosaic of blue, white, and brown areas.
A planet this big was impossible, so the sphere had to be hollow. Its density was about the same as air, with almost all the mass concentrated at the core.
They spiraled inexorably toward a depression, at what passed for the object's north pole.
   They weighed less here than on Earth's surface, but with their available fuel reserves, the object's gravity well extended far beyond any escape hyperbola. They couldn't return to Superspace from here.
   If only they could have harvested the gas stream, or if Lidal had ordered full thrust at 45 degrees, they could have landed nine levels higher. He'd waited a minute too long!
   They roared through the atmosphere in a pillar of fire, and splashed down hard in a shallow sea. Floating motionless on a waveless ocean that appeared to contain not a single atom of deuterium, they had calculated their future within the hour.
   "We're stuck on the outer surface of a small Dyson sphere," Ella had said. "It's almost 20 million kilometers wide, made of 675526 rectangular segments, each with a surface area of billions of square km. The gravity we feel is from a modified white dwarf star at the center. The effective pressure of the starlight, about five tons per square meter, or a few million times brighter than the sunlight at the beach - is keeping each segment afloat. They're made from a very thin and strong pseudo-material, possibly Quark Goop."
   The sea seemed too wide, like being at the bottom of a concave cup. Atmospheric diffraction made the theoretical horizon even more distant. A long light-strip dominated one side of the sky.
   "Adjacent segments are at different altitude ranges over the star," Lidal had noted.
   "That light strip is the next row of segments," Ella explained. "The bottom is a most efficient mirror. Most of the light bounces back to the star, reheating its atmosphere. The white dwarf is already ten times normal size, despite its crushing gravity. Less than one millionth of the light is reflected sideways to lower levels. The reflectiveness varies to create climate zones and weather."
   "The star is not quite bright enough anymore," Thurys had said. "The 'mirrors' don't just use light pressure to float. They convert a fraction of the light energy into direct thrust."
   "Nice trick," Ella said. "Billions of years ago, the builders started the sphere with only a few segments. They kept adding hovering carpets until they covered the available surface area. Fortunately for us, the segments are connected. The lowest ones are over the star's poles. From there they spiral outward, rising to maximum altitude over the equator. Gravity is highest on the lower segments, which have slightly deeper oceans to balance the starlight pressure."
   "The light output is too high for a white dwarf, even amplified by the mirror blanket," Lidal calculated. "To expand and maintain the sphere, the Builders periodically brighten the star by feeding it hydrogen. We had the bad luck to be caught in a gas stream. Fortunately we broke free."
   "Where are the Builders?" Thurys wanted to know. There were no other ships in the sea, no radio traffic.
   "They lost themselves in the world they created," Valmar had guessed. "Too much diversity."
   The crew's only hope had been to travel from segment to segment, slowly spiraling up and outward from the sunken polar region. Once they reached the highest equatorial level, they would make their escape. That area was in perpetual darkness, a simple mirror strip with no inhabitants - except vacuum creatures? They would cut off a large mirror piece, and scrape away any embedded ballast. Then they would use it as a solar sail, ascending straight up until they could Jump back to their departure point.
   They would return only a moment after their departure, which boosted morale. However, the millennia they had spent on Hoverworld would be inaccessible to future travelers.
   There was a slight problem: the size of Hoverworld. Their journey to the top would take 400,000 years.
   They rarely thought about that. The way to function was to divide their time into meticulously planned segments, a mental regime filled with four thousand centuries of useful activity.

   The grass blended into an endless expanse of dunefields. Valmar sensed space running out ahead. The sky was blue all the way to the distant, elevated horizon, but something behind the sky didn't reflect radar. An immensely wide and tall barrier, far higher than the clouds.
The Wall was only a few days away.

   Fifty hours of limited utility passed and were forgotten. The time was not experienced so much as relived, merging seamlessly into the memory of older days.
   Behind a final stand of tall trees, the universe seemed to end. A featureless wall rose higher and higher above the clouds before fading into the sky itself.
   Strange structures dotted the edge of the forest. They couldn't solve the mystery of the Wall sculptures. A few of the tallest had risen up all the way to the other side, but none had moving parts or controls.
For Mordos, the only way forward was straight up. The wall's clay-like pseudo-substance could be temporarily reshaped, and it even responded to electro-adhesives. The trained robot arms could "drill" four footholds per second and pull the ship three meters higher in the same time. The shallow indentations would eventually vanish. The climb, and the slightly shorter descent on the other side, took only about a week.
They felt the familiar excitement. Like any prisoner, they didn't mind working hard to aid their eventual escape, no matter how distant.
   At night, they occasionally saw free-moving carpet segments on unknown errands through Hoverworld, propelled mostly northbound by movable mirror strips hanging below each world segment.
If only they could ride one like a taxi under the mirror segments to their destination. But it wouldn't be able to take off again after landing to pick them up.
At least that was what they had thought, until they saw a carpet act like a reverse solar sail, somehow being drawn toward the light from a hanging mirror strip.
   Occasionally, two adjoining world segments would line up, and raise their atmosphere walls. A single unified domain would then experience several centuries of biological chaos, until the walls inexorably descended again.
Were that to happen today, they would be ecstatic (they welcomed any diversion), but raising the walls had a dark side: this was how new and improved species spread through Hoverworld.
   They all knew what that meant. Eventually the monsters would come, eradicating everything in their path. The lazy "Sleepers" they had found in one ancient valley, pink slugs with atrophied limbs and no detectable sense organs, wouldn't stand a chance.

   There was a void in their memories. Halfway through their journey so far, Mordos had crossed the Chaos Segments; NullZone; Hellland; Dragonheim . . .
   The first sign had been an insect-like creature charging their ship. Moving impossibly fast, the thing had left a long scratch on the hull before fleeing. Let loose on Earth, it could have killed thousands of people in minutes, but here it was at the bottom of the food chain. A week later, they found a cluster of eggs on a beach with almost indestructible shells.
   The sounds in the undergrowth got louder as they advanced through a savage wilderness. The trees got bigger, with more places to hide.
   A mass of whirling limbs plummeted from a towering trunk. The shock of the impact had strained the ship's geodetic endoframe. Valmar kept the scar on his forehead as a reminder.
   The roar of its fury had not affected their response time. In seconds, the inner hull might be compromised.
   A powerful electric current circulated permanently inside their high-energy Tokomak Fusor. Lidal had disengaged the magnets, and rotated a pulse constrictor to the exhaust bell. One of the creature's limbs had touched a thruster, closing a circuit with the ground. The crack of lightning had started a forest blaze (there was plenty of fuel), and the creature ran off in several pieces.
   After this encounter they had only traveled at night. There were no heavy isotopes on Hoverworld - apparently the Builders didn't want nuclear animals to evolve - which had limited their available power. They managed to jury-rig an automatic cannon, but for a while their progress had slowed to walking speed. Their seismometer gave little warning against flying creatures.
The largest monsters could be spotted from thirty kilometers away, necessitating long detours. Some were like huge machines that tore up the landscape. Muffled roars and howls penetrated the almost soundproof hull.
Other entities were microscopic but no less vicious.
   Almost halfway through this wasteland, when the view from his control seat became worse than his nightmares, Valmar had guessed they wouldn't make it. They were forced to cut a path through tangled undergrowth, where some of the branches fought back.
Lidal had ruthlessly led them through the mad jungle, his finest hour. He found a few weaknesses: the creatures' dislike of inert elements, and extreme cold, and water and dust sprays.
   The number of monsters had temporarily decreased, the calm at the eye of the storm. The shapes became stranger and less organic. Towers of stone and city-sized hollow boulders dotted the landscape. The colors had been leached from the world.
That had been their time of greatest danger. There was something terrible here, but they had never found it. Perhaps it had been sleeping.
   One night, their fifth crew member had vanished without a trace. No doubt he or she had recycled themself, and altered the ship's records to erase all evidence of their existence.
The remaining crew had decided to delete their memories of this individual until their return to Earth.
Coming out the other side of Hellland was easier, as if their sacrifice had bought a degree of good fortune.
   If they ever saw another monster zone ahead, they would construct a large bunker, and follow Lidal's hibernation-beacon plan. Nothing else could be as bad.
By now they had accumulated a lengthy catalog of wonders and anomalies.
They had seen evidence of "worldquakes" that could turn granite into fine powder.
One ocean had appeared to be ordinary water as they crossed it at an altitude of fifty centimeters using their surface-effect thrusters. As spray accumulated on the hull, the weight of the incredibly sticky compound began to drag them down. When they finally reached the beach (creatures were playing in the surf quite unbothered by the hyperglue) their cruising altitude had been reduced to twenty centimeters.
They joked about such incidents. Even the multiple hurricanes stacked like counter-rotating platters became a pleasant memory.

   "How many monsters could evolve in five billion years?" Valmar asked. "We haven't seen the worst yet."
   "More proof the Builders were insane," Thurys said. Her dream was to survey 50% of Hoverworld, so mankind could claim it under universal salvage laws. First she needed to prove the Builders were extinct.
   Very rarely, they came across a monument. Ancient pillars stuck like bones in a dry valley. An abandoned archway in a featureless desert.
   None of the creatures they had encountered showed the slightest trace of civilization. Their cruel, natural brilliance couldn't be expressed in language or culture.
   "Maybe they evolved into a race of post-emotional gurus," Valmar suggested. "A monastery at the end of the great spiral."
   Thurys shrugged. "They won't mind if we colonize the rest."

   Tonight they would start scaling the Wall. The external claws and ratchets were assembled, and the ship's small Air Force of external robodrones (locally manufactured with great difficulty) had returned home.
They waited in the shade of the Foundation Trees, so tall their branches formed an artificial sky. Because of their extended root systems, there was plenty of room between the slender, almost airy trunks.
Despite a surface breeze the telescope detected no motion in the leaves.
   Through his improvised mind implants, Valmar studied the greenish web above. So many patterns they didn't understand. How could they know the trees weren't aware?

   The realization came slowly, like waking from a dream. He saw every piece of evidence in a new, paralyzing light.
This place was not what it seemed. Everything had been laid out long ago. Perhaps eons ago.
The tree canopies surrounded them like a vast stadium. Those two valleys provided immense sightlines with Mordos at their focus.
   They were being watched.
   He was beyond terror, in a realm of numb apathy. After half a minute he still hadn't pressed the alarm. He tried to move one finger.

   Valmar could barely see the anomaly against the leafy background. An arrangement of sticks suddenly became a different arrangement. That inverted pendulum (slowly turning?) might be its head.
He never armed the cannon or the fusion magnets. It would have been pointless. This creature could move mountains.
Like them, it was traveling to the next segment.
   Bump!
There was a small vibration on the top deck, and the crew assembled in the Bridge around Valmar as the belated alarms sounded. Lidal jumped in the command seat, inserting his own mind plugs. Valmar was too absorbed to notice the commotion around him.
Finally, he turned to the sideview cams, craning his attention up the ship's hull.
A dark piece of debris came rolling down the side, tumbling in a not-quite-random way.
Exactly how long had it been up there? He tried to think, but there were empty spots, forbidden gaps in his memory.
The gray-brown husk bounced on the moss below, where it settled in a peculiar shape.
   The first being was out of the tree now, extending what might be long arms. In the evening light, its shape was vaguely humanoid, but the impression vanished when it started to run. It grabbed the now motionless object that vaguely resembled an upright mummy. Then it turned and was gone.
   There was total silence in the cabin. "We've been used," Lidal said at last. "It used us to transport that thing. What was it?"
   "That was its mate," Ella said at once.
   "Genetic material or encoded knowledge," Thurys replied.
   Valmar scanned the woods. They were definitely alone now. The alien had lost all interest in them.
Perhaps it could have helped them escape from Hoverworld, but gratitude was such a primitive emotion. This being had transcended primitive emotions eons ago.
   "Was that a Builder?" Ella asked. "It looked at least a billion years old."
   "It may have been a descendent of the Builders," Thurys said. "This world became too big for them . . . the Babel Syndrome. They fragmented into countless species . . . thereby forfeiting their sole claim," she continued.
   Valmar finally spoke without turning. "Those two creatures may have been the Builders' species by themselves," he said. "Think of how many cells large organisms have. Why should every cell have the same genetic code? It's possible for a single individual to contain the complete genetic diversity of its species."
   Lidal said: "I don't know what it was, but it explains why this world appears uninhabited: it needs a lot of space."
   "How could it have effortlessly manipulated us?" Thurys pondered.
   Still slightly hypnotized, Valmar scanned their hull. He had inspected every square centimeter many times. Near the top of Mordos was an acid-worn stain, where something big had been stuck for centuries.
   What else had been hidden, while humanity was still trying to learn how the universe worked?
He prayed they hadn't been forced to break the ship's seal, and then falsify their logs.
The one constant in their lives had been predictability. Instantly, they had learned a greater truth.
The wilderness would never seem empty again.