The Hollow Earth’s Lungs

The World’s Largest Cave: It Has a Forest, a River, and Clouds Inside

Prologue: The Last Transmission

Day 17. Coordinates redacted. This is Dr. Elara Voss, lead geologist of the Hollow Earth Consortium*. We’ve… found something. The cave isn’t just a cave. It’s a biome. A living, breathing organism. The clouds—they’re not water vapor. They’re spores. And they’re aware. Do not send rescue. Repeat: Do. Not. Come. Heed the—

Audio recovered from Expedition Team #7, 2022

Chapter 1: The Door to Nowhere

They called it Hang Sơn Đoòng on the maps, but the Viet Cong soldiers who’d first stumbled into its throat in 1991 had another name: Hơi Thở Quỷ—The Devil’s Breath. Now, 33 years later, the cave’s true scale still defied drones, satellites, and human arrogance.

Zoë Carter adjusted her harness, her gloves slick with sweat. Below her, the entrance gaped like a toothless scream, 650 feet wide. Remind me why I agreed to this? she shouted over the rotor wash of the helicopter.

Because you’re the best damn biologist on the payroll, said Malik, their lead climber, grinning through his salt-and-pepper beard. And because of this— He gestured to the abyss. —eats National Geographic cover stories for breakfast.

The team descended: Zoë, Malik, a documentarian named Jules with a death grip on his camera, and Kiet, a Hanoi-based geologist who hadn’t spoken since they’d left basecamp.

The first anomaly hit at 1,200 feet.

Uh, guys? Jules panned his light across the wall. Since when do caves have tree roots?

Zoë traced the thick, woody tendrils snaking down the limestone. They pulsed faintly, as if sap flowed beneath their bark-like skin. These aren’t roots. They’re hyphae. Fungal networks. But… She sliced a sample with her knife. The tendril bled iridescent blue. This isn’t mycology. It’s… something else.

A rumble echoed from the depths. The air tasted metallic, charged.

Kiet finally spoke: We should turn back.

Malik laughed. After flying 9,000 miles? Not a chance.

Chapter 2: The Forest That Shouldn’t Be

By day three, they’d mapped a chamber larger than Manhattan. A jungle thrived in perpetual twilight: 100-foot trees with bioluminescent leaves, carnivorous orchids that sang in high-pitched trills, and a river so clear it mirrored the cave’s ceiling—a starless night speckled with glowing clouds.

They’re not clouds, Zoë realized, catching a wisp on her glove. The particle squirmed, revealing microscopic cilia. They’re colonies. Organisms floating on thermal drafts. Like plankton… but airborne.

Jules zoomed in. Holy shit. They’re swarming the light.

As Malik hacked through a wall of vines, Kiet hung back, snapping photos with a disposable camera. You know why no one returns? he muttered. The cave rejects modern tech. GPS, radios, batteries—all fail. Only analog survives here.

Zoë frowned. You’ve been here before.

Before Kiet could answer, Jules screamed.

A vine had lashed his ankle, dragging him toward a blooming flower the size of a minivan. Its petals peeled back, revealing rows of translucent teeth. Malik lunged, machete raised, but the hyphae from the walls writhed to life, binding his arms.

Zoë grabbed Jules’ pack, yanking him free as the flower snapped shut on empty air. The spores around them flared angry red.

It’s defending itself, Zoë breathed. The entire ecosystem—it’s connected. A single organism.

Kiet stared at his hands, now dusted with glowing particles. Not an organism. Intelligence.

Chapter 3: The River of Echoes

The river’s whispers were wrong. Not the gentle babble of water over stone, but a low, wet gurgle, like something drowning in its own throat. Zoë’s boots sank into the bank’s black silt, each step releasing the sweet-rot stench of decay. The bones began as fragments—a rib cage here, a shattered femur there—but soon they piled like driftwood. A mammoth tusk, fossilized and quartz-veined, jutted from the mud beside a modern climbing harness, its buckles crusted with rust.

Malik crouched, brushing dirt from a corroded helmet. Expedition Team #3. Vanished seven years ago. He turned it over, revealing a deep, jagged dent. “They never made it this far upstream.

Because this is where the cave starts fighting back, Kiet muttered, lagging behind. His eyes darted to the spores swirling overhead, their bioluminescence dimmed, as if listening.

Jules aimed his camera at a skeletal hand clawing upward from the sediment, its fingers still curled around a leather journal. The pages crumbled like ash when he pried it loose, but a single sketch fluttered free: a humanoid figure, limbs stretched grotesquely long, its head a cloud of spores. Freaky Picasso shit, he said, zooming in. “You think it’s a warning?

No, Zoë said. A blueprint.

The river widened abruptly, spilling into a lake so still it mirrored the cavern ceiling—a false sky teeming with glowing clouds. Jules dipped a hand in, yelping as the surface tension clung like gelatin. It’s not water. It’s thick.

Then the spores descended.

Not a drift, but a coordinated plunge. Millions of particles coalesced into a vortex, humming with a sound Zoë felt in her molars: radio static, overlapping voices, a dial tone from the void. The pillar contorted, forming a faceless mouth.

Why… do… you… bleed?

Zoë’s nose erupted—a hot, metallic gush. Malik crumpled mid-scream, his veins bulging blue beneath his skin. Jules kept filming, even as his lens cracked under the spores’ pressure. It’s talking! Holy Christ, it’s—

Flesh… fragile. We… adapt.

The pillar slammed into the lake. The thickened water thrashed, and the things that surfaced were neither alive nor dead.

A bear skeleton, its ribs knit with glowing hyphae. A tiger, its skull blooming fungal flowers where eyes should be. And a human figure, its pelvis fused to a stag’s spine, fingers elongated into root-like tendrils. Their hollow eyes locked onto the team, and the bear’s jaw creaked open:

Join.

Kiet’s disposable camera hit the ground. They’re not hallucinations. They’re… archives. The cave absorbs what it kills. Rewrites them into itself.

Malik writhed, clawing at his throat. What’s… inside me?

Zoë dragged him backward. Nothing we can cut out.

Chapter 4: The Light That Lies

Malik’s veins glowed through his skin now, a bioluminescent roadmap of infection. He thrashed in his sleeping bag, muttering in languages none of them knew.

We’re leaving, Zoë said, stuffing gear into her pack. Now.

Jules blocked the tent flap, camera rolling. Are you insane? This is the biggest discovery since—augh!

She slapped the lens. Your Pulitzer won’t matter if we’re part of the exhibit!

Kiet stood apart, staring at the lake. It’s too late. We’re already claimed.

The light came then—not the warm gold of sunrise, but a surgical white beam spearing down from the ceiling a mile above. It illuminated a stone archway etched with spirals and claw-like glyphs.

Kiet traced the symbols, his voice hollow. Chữ Nôm. Ancient warnings. ‘The door closes at dawn. The mind opens only once.

Door to what?” Zoë gripped his shoulder.

His smile was faint. To where it thinks.

The climb burned Zoë’s arms. The archway opened into a cavern that defied scale—a cathedral of pulsating spores, their light throbbing in time with her heartbeat. At the center hung a mass of writhing fungi, veined with what looked like dendritic tissue. It pulsed like a brain.

We… are… the earth’s memory, the spores boomed through Jules’s camera, now glitching violently. “Flesh… weak. We… perfect.

Jules edged forward, lens focused. “It’s alive. It wants to communicate—

The mass contorted. Hyphae speared his chest, lifting him off his feet. His scream died as spores poured into his mouth, his nostrils, his eyes. His skin crackled, hardening into bark; his irises dissolved into milky mycelium.

“Run!” Kiet hauled Zoë back as the cavern shuddered, the archway crumbling.

Chapter 5: The Last Breath

Dawn stained the jungle blood-red. Only Zoë and Kiet emerged.

Military helicopters churned the air. Journalists shouted questions.

What do we tell them?” Zoë’s voice was raw.

Kiet lit a cigarette, the flame steady. That the cave is empty. That monsters aren’t real.

And Malik? Jules?

Gone. Like Team #3. Like my brother in ’91. He pressed a film cartridge into her palm. But the cave remembers. It always does.

That night, Zoë developed the film. The last frame wasn’t hers: a young Kiet stood beside the fungal mass, unaged, unharmed. The date scrawled in the corner—1991—matched the cave’s first official discovery.

On the back, his handwriting: The cave chooses who remembers. The rest become its voice.

Outside her window, the spores glinted in the moonlight, drifting north.