Clearly, the planet wasn't as inert as she'd thought. Something was going on that she didn't understand. It bugged her. She relayed the recordings she'd taken of the building's interior to the ship. “Can you make anything of these? If they're stars and planets, maybe you can work out a dating from the degree of sidereal shift.”
“I'll begin the analysis. Are you going back inside?”
“Oh yes.”
“It doesn't appear I'll be able to contact you if any threats present themselves out here.”
“Just be ready to leave in a hurry. There's nothing more to report from the mesh?”
“Nothing new. We do now know that it surrounds 99.8% of this solar system. Also that it isn't a perfect sphere, as if impacts have buckled it at some point, but I'm no nearer any understanding of its nature or purpose.”
“Perhaps it's art.”
“Art?”
She shrugged, although the Dragon wouldn't be able to see the motion. She stepped back from the blinding light into the darkness of the ancient structure.
Once she'd captured every detail of the wall decorations, she walked to the centre of the triangular space to study one of the lumps of jagged rock that had crashed through the structure. It was clearly not a projectile weapon of any sort. A spectrographic analysis suggested it was similar in composition to the planet and the few specks of space debris they'd harvested, mostly unrefined silicates and heavy metals. Her best guess was that the impact had been part of the normal processes of planetary bombardment and coherence rather than a weapon in some attack – which did suggest the structure was old. With the planet and star formed, such impacts would be rarer, and the chances of a direct hit on what was, compared to the planet, a tiny structure, rarer still. Although perhaps the planet's proximity to the gravitational pull of the solar mass made a strike more likely.
In the precise centre of the room, directly beneath the apex, she found something she'd initially missed: a thin rectangle of clear floor in the carpet of dust, as if something had been standing there until very recently. It was two metres long, five centimetres wide. As she approached, she detected the faint stirrings of an electromagnetic signature from the floor. She froze, senses alert, expecting attack. Once again, nothing moved.
Warily, she took another half-step. A white rectangle three metres tall slid out of the ground in front of her, bright in the low light, noiseless in the vacuum. She stepped backwards, alarmed, heart hammering. No attack came: instead, the rectangle slid back down into the floor and was gone.
She moved forwards again, and it rematerialized.
Now she could see detail within the light of the rectangle. What she saw made no sense whatsoever: it appeared to be a doorway through which she could see the interior of a second hallway, receding into an impossible distance and lit by round lamps that hovered in the air.
“Ondo, are you seeing this?”
“I am.”
“It's incredible.”
She stepped warily around the oblong. From side-on, the vault through the doorway disappeared from view and then reappeared on the other side: a vast cavern seemingly contained within the narrow plane of the rectangle.
“Some kind of portal.” she said. “Have you ever seen anything like this?”
“Concordance have nothing like it. It may be an illusion. A projection.”
Selene stooped to pick up a handful of dust and threw it through the door. She thought it would disappear, or bounce off, but it passed through the frame as if it were perfectly normal. A scatter of the dust fell to the floor of that other chamber. When she walked around the door to see through it from the other side, the dirt she'd thrown in was still there.
“Seems it's real,” she said. “I'm going to go through.”
Ondo was inevitably cautious. “You don't know if you'll be able to come back.”
“I'm not going to come this far and not try. If I get trapped the Dragon will give up waiting eventually and return to you with the data I've recovered. And don't you want to know what's through there?”
“I do, of course.”
She hesitated for just a moment, then strode through. Turning, the oblong frame remained reassuringly solid, the pyramidal chamber visible through it, her own boot prints in the dust, the slanting light from the broken walls. Had she been transported to some vault deep underground? Or to somewhere else completely? She had no way of knowing. She backed away a step, and another, and, just as before, the door slid from sight. Her heart raced a little more quickly. She really did not want to be trapped inside an impossible alien structure of unknown purpose. She instructed her heart to calm, quieting her fight/flight response, then moved back towards the door. It dutifully reappeared, the surface chamber visible once more. She stepped through two, three times until she was convinced she wasn't going to get trapped, then crossed into the inner lamplit vault one more time. She walked away from the glowing frame, letting the door disappear behind her.
The second chamber did not look damaged; there was no bombardment wreckage, no dirt other than the grit she'd thrown. The floor and walls were constructed from white stone blocks that interlocked in complex and irregular ways. The room looked freshly built, edges sharp, surfaces shining. It was maybe thirty metres wide and a hundred high, the walls arching overhead to meet at a high apex. It curved horizontally, too, as if it might be a complete ring. A thrill of something between fear and awe grew within her. She'd experienced something similar on a tourist visit to the Great Temple in Caraleon, something about the soaring architecture and the ancient quiet sending a shiver of wonder through her. What was this place?
The hovering light globes receded in two arcs away from her. Underneath them stood a winding line of something like stone plinths, bare and cylindrical, each a metre or so high. An object
