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// Chapter 41: Pearlescent 
// Story: Sisters of Willowbrook 
// by Starscribe 
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Something caught her from behind, a pair of muscular legs that wrapped around her own forelegs. The weight brought them together in the air, then pressed Firefly's wings down. For a few seconds she continued in the same spiral, flying wider as their angular momentum more than doubled. 

But Rainbow Dash knew what she was doing. Force pressed down on Firefly, as intense as any Earth rollercoaster. 

She stopped screaming, before finally coming to a stop in the air.

"You good?" asked the mare. At her nod, Rainbow let her go, freeing her to hover under her own power. She could still manage that, though her body shook from the exhaustion of her whole ordeal. 

Physically speaking, this flight was far more demanding than escaping the mine. But she could hover in place, facing the mare. "That was... the craziest thing I've ever done! I didn't know anything alive could move that fast!

The mare looked back, flipping the goggles out of her eyes. Even she was breathing heavily, though a sense of constant pride radiated from her like the heat from a flame. "Yeah, well. Fast is kinda my thing." 

She patted Firefly on the shoulder with one hoof. "Keep practicing, filly. I don't know very many grown mares who could keep up with me during a flight like that. You've got talent."

It didn't matter that the exterior clouds were dark gray, consuming most of the light. From a pony like this, those words were like stepping into the sun. Firefly didn't understand magic, and she couldn't cast incredible spells. But she wasn't useless.

"What's in here, anyway?" The mare turned away from her, focusing on the strange structure they had entered. Firefly did too, though for very different reasons. She needed to find somewhere to land and catch her breath before she collapsed.

The structure was unlike anything she had ever seen in the Cumulus Maze before. Most cloud houses were just that—structures using clouds as a substrate, built on fluffy foundations. The design was not that different, just the materials.

This building was more like a two-layered shell, with the thick external thundercloud separated by a narrow "pipe" of still air from a rounded cloud building. What she thought to be a flat wall while she was flying for dear life was actually a subtle curve, matching the rounded shape of the thunderhead from outside.

Without a word exchanged between them, they flew around this structure, searching for a way in.

The design was leagues beyond any cloud building she'd ever seen. Instead of simple pillars, this one used an intricate lattice of ice, forming a delicate upward spiral of thin sheets. 

Thin, but incredibly strong. Rainbow hammered one hoof on a clear section, then pulled back in pain. There wasn't even a crack.

"Twilight told me this town was gonna be weird," she said. "I didn't know how much. Have you seen places like this before? How do we get in?"

Firefly didn't want to answer, or else give the mare regrets about their trip. The last thing she needed right now was word of this particular adventure reaching Dusty. He was already nearly a nervous wreck after Firefly's adventure in the mines.

"I saw spirals like this before," she began. "Based on the way it curves, it should point outward near the top. Maybe there's an opening there?"

"Worth a short," the mare said. "One last flight up." She chuckled nervously. "Sure hope Twilight doesn't have anything crazy planned for tonight. Haven't worked this hard since academy training."

They flew upward, with Firefly occasionally resting her hooves against the building. Even a few seconds when she wasn't flapping helped. The effort was exhausting enough, but the altitude really made things difficult. They must be higher up than she'd ever been in her life.

Curious that the clouds weren't colder. The thunderhead blasted her with snow on her way in, but this little pocket of air was downright comfortable.

Eventually they made it to the top. Thousands of thin icy supports came together in an interlocking spiral like a basket, held together by a single ring of strange red metal. But there was an opening inside it, finally giving them a path to glide down.

It also glowed with incredible light and heat, enough that Firefly closed her eyes as she approached. She sped up, flying quickly so it wouldn't bake her alive. Hot air rose out of that opening, forcing her to tuck her wings in for another dive.

It looked like a city, or maybe a town. There were a dozen internal structures, each one as beautiful as the exterior. They were formed of ice like spun glass, with a faint metallic shimmer to them. They were skyscrapers, though their designs were unfamiliar. Maybe in the feverish imaginings of a futurist could structures be made so beautiful. 

They had stained the ice in different ways, producing “windows” with an internal view, as well as opaque sections without. Murals were formed here, showing natural scenes. Mountains, fields of swaying wheat, crashing waves and tropical islands. 

The ground was strangest of all. There were no roads or paths between buildings, but strangely blue-tinted plant life, swaying in a warm breeze. A few ponds were visible as well, with a thin algal film staining the water. 

The city had no people, though. Firefly saw only the occasional bird here, mostly pigeons. They nested among the blockier buildings, or in places where the icy windows were shattered.

But that makes sense. In Equestria, all birds can walk on clouds. Rats could never infest the city, they would fall right through.

Rainbow Dash found a wide balcony, connected to the tallest structure in the dome. That also meant it was the shortest distance to fly before landing on something.

Firefly collapsed onto the solid cloud surface, spreading out her body and letting her wings hang limp. She felt utterly exhausted, drained more than any high school fitness test she could remember.

The mare was a little more dignified, settling onto her haunches. Her wings sagged though, and there was no more glow to the feathers. She'd been exhausted too. "Can't hear the storm from in here. I bet during the day the sun would shine in through that hole."

Firefly nodded. Something still heated the metal above them, producing a glow not unlike the orange of sunset. Without a storm, Willowbrook would be having exactly that. But how could it regulate the light inside the dome without any machinery? 

It was hard to gauge the space—maybe a kilometer in radius? It was much smaller than the thundercloud from the outside. But that was plenty of space for buildings. Hundreds, maybe thousands of ponies could live in here.

"Well that was something... Firefly, you said?" The mare stood up, as though the tremendous energy of their flight was already coming back to her. Maybe it was, with the incredible strength she had. "Great job getting in here. Wish we had time to explore all this, but I really shouldn't. We're on an important mission from Princess Celestia, and it wasn't about inspecting cloud ruins."

You aren't the least bit curious about what could be inside?

Firefly stood too, though she wasn't recovering as fast. With other ruins she could always come back in a few hours—but she knew instantly that she would never stand a chance of getting into this place without the pegasus slicing through the wind ahead of her. Maybe with another decade of practice. At least she had something to aspire to.

"We should at least look inside one building!" She reached to the side, where she would usually keep her exploration satchel. A place to carry what she scavenged, the tools she used, maybe a flashlight. But she had nothing there, of course.

Even if she hadn't dropped her bag, it would just be boring notebooks and school supplies. "Can your mission for the princess wait a few minutes?" She took one step back along the balcony, which was open. In its own way, this building might be a palace. Princess Celestia can't have anything as nice as this living on the ground. 

"Well... a quick look. Twilight would probably ask what I found. If I didn't give her an answer, we'd probably have to go chase this storm after we finished in the dumb mine."

They walked together through the open doorway. Firefly was equally stunned by her surroundings as she was the pony's words. Sent by the princess to investigate a “dumb mine.” That could only mean one place. It also meant that Equestria was onto them. They had managed to identify the location of Lilac's magic, and get a team out to investigate it in only a day.

The castle itself was appropriate to the glory of its city. The ones who lived here favored a silhouette style, with mosaics of colored ice-chips on the walls but plain cloud floors. Tattered banners hung from regular points, and the palace had some of its own light too.

The figures on the walls were clearly ponies, though not pegasi. They had horns as well as wings. This place had once had Alicorns who ruled inside it, then. 

As incredibly skilled as her flight had been, her companion didn't show a lick of academic curiosity. She walked right past the art, stopping only when they reached a set of thrones.

There were six of them in a semicircle, at varying heights. Each one had a different gemstone set into the cloud material. They glowed faintly as Rainbow and Firefly approached.

Firefly hopped up onto the raised dais, reaching towards one of the glowing stones. Rainbow caught her by the hoof, holding her back. "Careful, filly. I've read enough Daring Do to know what happens when you mess with the ancient artifacts in the magical sky castle. How about we just look for now, let the archeology ponies poke at it."

She didn't fight, backing away from the seats again. Curious how the gemstones responded to their presence, though. "Do those Daring Do books talk about who could've built a place like this?"

The pegasus grunted with disinterest. "Eh. Nopony really knows, that's part of the mystery. Sometimes the old ponies set up magical guardians, and they all liked traps. But if we just visit, they won't go off." She spread her wings, stretching from one side to the other. "My friend's a real brainiac, she might be able to tell you. Just try to remember that shape right there. That looks important."

Firefly looked, and froze. She had seen a version of that exact logo thousands and thousands of times, every time she saw the Lightless Star members in person. It showed a tall, tapering tower, superimposed on a huge eye. Only the eye on the banners was open instead of closed.

By the time she realized what was happening, Rainbow was halfway to the exit. She scampered after her, leaving the dark space behind.

There's so much stuff in here. How can I get back without getting killed by a hurricane?

"So why'd you come looking for a mine, Miss Rainbow Dash?" she asked. "Don't you just hate being underground?"

The mare met her eyes, looking instantly sympathetic. "Guess you've been underground before. It's awful, but somepony had to come with her and Rarity." She lowered her voice to a conspiratorial whisper. "I'm not supposed to tell any of the locals, but you can keep a secret, right?"

She didn't look at her eyes, but her wings. "Yeah, I thought so." She draped one over her shoulder, pulling her close for a second. "I can feel it about you—your loyalty. That's strong stuff. You'd do anything to stand by your friends."

She nodded, baffled. What did loyalty have to do with anything? "I'd go to the end of the world for my friends. I'd fight anything, and maybe even come back one day."

The mare gave her one last pat with her wing, then let go. "I told Twilight that Celestia was probably worried about nothing. She got all scared about the ponies of Willowbrook. Don’t tell her I said this either, but she thinks you're all creepy weirdos." She lifted both wings as she said it, in a gesture Firefly instantly understood. "But you find harmony no matter where you look.

"In faaact...." She grinned sideways at her. "We're on an important mission for Princess Celestia. I know the first thing Twilight would want to do is find somepony from around here we can trust to show us around. You ever heard of the... Cyan Mines?"

Firefly nodded without thinking. "I've heard of 'em. They've been closed since before I was born."

"Oh, yeah. Perfect place for nefarious evildoers to set up their secret base. I just know Rarity’s gonna love it.”