Senja hung at the mouth of Luweng Ombo while the sun had not yet completely left the karst slope. His body was outside the chasm, but both legs already extended into empty space. Beneath him, layers of limestone walls descended toward a darkness that revealed no bottom.
He checked his descent gear one more time.
UIAA- and CE-certified static kernmantle rope ran from the anchor point behind him, through the descender, then vanished into the shaft. His sit harness was secured tightly to a chest harness that kept his body upright. The Croll, hand ascender, cowstail, carabiners, headlamp, radio, and emergency gear had all been checked. No buckles were loose. No knot had been left without a second inspection.
In vertical cave exploration, there was one rule that could never be broken.
One rope, one person.
Not two people at once. Not one person following too closely because he was afraid of being left behind. If something happened to the rope, the falling load had to be limited to a single body. The rule was simple, but in a place like Luweng Ombo, simplicity was often the last line between procedure and disaster.
“The main anchor is secure,” Ucok said beside the anchor point. “The webbing hasn’t shifted. The carabiners are locked. The rope protector is still covering the section rubbing against the edge of the rock.”
Senja turned. “Any friction?”
“None yet. I’m monitoring it continuously.”
Oscar knelt beside the coil of rope. He wore a harness and cowstail already connected to the safety anchor. His hands fed out the rope little by little, making sure no loop could snag on the rocks or roots along the edge of the chasm.
“Radio’s on,” he said. “Whistle’s ready too. If you don’t answer, I’ll assume you’re busy saving yourself.”
“If I don’t answer, don’t come down looking for me right away,” Senja said.
“I know. I’ll yell first.”
“Don’t yell.”
“Fine. I’ll yell in my head.”
Ucok sighed. “That won’t come through the radio, Mas.”
Senja gave a faint smile, then focused on the route below. He was the pioneer, the first person to descend. His job was not merely to reach the bottom, but to inspect every section, making sure the rigging, anchors, and direction of the rope remained safe for the two people following him.
“Starting down,” he said.
He shifted his weight onto the rope.
For a moment, the world above shrank into a circle of light surrounded by forest. Then the edge of the chasm receded. Senja’s body hung free between the rock walls, his headlamp the only eye moving through the darkness.
He lowered himself in a controlled manner with the descender. One hand managed the friction while the other maintained his position. His boots touched the wet wall, then slipped free again when the rock surface changed into an empty alcove. In several places, the wall jutted outward, causing the rope to pull his body away from the rock. He let the equipment do its work, lowering himself inch by inch without allowing speed to take control.
The first section ended at a rocky ledge large enough to stand on. Senja stopped, locked his position, and inspected the next anchor. The old webbing shown on the map was no longer in use. He secured himself to a solid piece of bedrock, transferred the system to the next section, and continued downward.
At a greater depth, the light from the cave mouth turned into a pale line. The sounds of the forest disappeared. All that remained was the sound of his own breathing, the rope rubbing against the descent gear, and drops of water falling from above without ever revealing where they landed.
“Senja to top,” Oscar’s voice came through the radio, broken by echoes. “Status?”
“Second section is secure. There’s seepage from the east side. The rope isn’t in the flow.”
“Distance to the bottom?”
“Still a long way.”
Oscar fell silent for a moment. “Your answers are always reassuring in exactly the wrong way.”
Senja did not reply. He was passing through a narrow section as water dripped onto his helmet. Below, the vertical space opened up again. The rock walls looked like the jaws of a giant beast clamping around the rope. He regulated his breathing, locked the descender, then moved his cowstail to the anchor on the next section.
Advanced SRT left no room for careless movements. Every transfer had to be done in the proper order: lock, attach the safety, transfer the load, check again, then open the system. A small mistake could leave someone hanging without a stable position, or worse, cause them to lose control above empty space.
Senja descended past the final section toward late afternoon. When the soles of his boots touched the bottom, the sound that had seemed distant all this time suddenly grew immense.
An underground river flowed between fallen boulders. Its water was black beneath the lamplight, moving toward a wide horizontal passage. The cave walls were wet, covered with a thin layer of moss and pale green growth that could survive only on seepage, not sunlight. A few small plants clung far above, on sections of wall that might still be touched by the light of dawn and dusk. There was no forest at the bottom. Only collapsed karst, wet rock, cold air, and tiny organisms that darted away whenever his beam passed through a crevice.
The darkness there felt solid. Drops of water sounded one by one. From the passage ahead, the roar of the river filled the space like the breathing of a sleeping creature.
Senja pressed the radio button.
“Senja to lower base camp. OFF ROPE.”
A few seconds later, Oscar’s voice answered from above.
“Received. Second person may descend.”
Senja secured the end of the rope, checked the lower anchor again, then switched on an additional light. He stood beside the river, waiting for a second light to appear in the darkness.
Oscar descended without significant trouble. His body looked small between the vertical walls, but his mouth kept working throughout the entire descent.
“If this is what you call a view, I’d like to file a complaint with the travel agency.”
“Don’t look down for too long,” Senja said over the radio.
“I’m not looking down. I’m looking at the possibility of my life ending.”
“Then you’re still looking down.”
Oscar reached the bottom breathing heavily, but both feet landed firmly. He immediately locked the system and detached himself from the rope.
“OFF ROPE,” he said. “I’m still in one piece. A little older, but in one piece.”
Ucok was the last to descend.
He inspected the anchor one final time before entering the system. All remaining equipment was tidied away. The spare rope was secured. The rope protector was checked to make sure it had not folded over. Even the radio was stored inside a waterproof layer.
“Take it slow,” Senja advised. “We’ll monitor you from below.”
Ucok nodded, then began descending the route.
At first, everything went smoothly. But when he reached the third section, the sound of rain came through the radio. It was not rain falling around them, but rain on the surface, carried by the wind into Oscar’s microphone.
Ucok stopped.
“Mas Senja,” he said, “it’s starting to pour up there.”
Senja looked at the thin stream that had just appeared on the wall beside him. Water crept down over the rock, at first like a clear line, then growing into a thicker flow.
“Don’t continue yet,” Senja said. “Lock your descender. Find a position sheltered from the direct flow.”
Ucok locked the device and pressed himself against the wall. Above him, something rumbled. Rainwater falling across the karst surface had begun searching for the fastest route to the bottom of the cave. Within minutes, a small seep could turn into a sudden waterfall. In a vertical cave, a flash flood gave little warning.
Oscar heard the sound through the radio. “The main rope is still secure. But water is starting to cross the fourth section.”
“Ucok, don’t move until the route is clear,” Senja said. “Hold your position. Don’t try to speed up your descent.”
“I understand, Mas.”
“If the flow gets stronger, we’ll change procedure. Stay attached to the main system, use your cowstail for additional protection, and wait for instructions.”
“Okay.”
The rumbling drew closer. Water burst from a crack in the wall above Ucok, striking the rock several meters away from him. The rope trembled lightly. He regulated his breathing, but every breath felt cold and wet. His headlamp caught the falling droplets like shards of glass.
“Ucok,” Oscar called, “are you still safe?”
“Still safe, Mas. It’s just starting to get pretty wet.”
“If necessary, I’ll send you an umbrella.”
“Just leave the umbrella up there, Mas.”
Senja held his breath. The joke sounded thin, but it was enough to keep Ucok’s voice steady.
The rain continued for nearly twenty minutes. The water then began to recede, leaving a rushing flow that still soaked part of the route. Senja checked the changes from below and told Ucok to descend at the right moment, passing through the section hit hardest by the water.
“Now. Descend slowly. Stop at the next anchor.”
Ucok opened the descender. His movements were careful, but his body spun several times when the flow struck his shoulder. He held the rope with both hands, braced his boots against the wall, then moved again. Once, his foot lost its hold and his body swung out into empty space.
“Stop!” Senja shouted.
Ucok immediately locked the device. His cowstail went taut as he clipped himself to the anchor. For several moments he simply hung there, soaked through, his breathing harsh over the radio.
“I’m safe,” he said at last.
“Check your gear.”
“Descender secure. Carabiners secure. Cowstail attached.”
“Continue.”
He descended again. Every meter felt heavier than the last. The water made his gloves slippery, and his arms and shoulders began to tremble, but he did not take shortcuts. He stopped at every anchor, locked the system, checked the connections, and continued only after Senja gave the signal.
When Ucok’s lamplight finally appeared above the last section, Oscar stood beside Senja.
“If he makes it to the bottom,” he said, “I won’t make fun of him for at least an hour.”
“Write that promise down.”
“I didn’t say what happens after an hour.”
Ucok reached the lower anchor with great difficulty. Senja helped guide his body away from the flow while Oscar held the rope clear of the sharp rocks. Ucok locked the system, transferred his cowstail, then stepped down onto the flat rock beside the river.
Both his knees hit the ground immediately.
“OFF ROPE,” he said hoarsely.
Senja immediately checked his helmet, harness, and hands. There were no serious injuries. Only scrapes on his palms, bruising on his shoulder, and clothes soaked through to the skin.
Oscar handed him a water bottle. “Welcome below. Our travel agency doesn’t accept complaints.”
Ucok drank, then stared at the black river before them.
“If I’m being honest, I’d like to complain just a little.”
“Go ahead.”
“It’s a beautiful place, but the entrance is outrageous.”
Senja stood and aimed his light down the horizontal passage. Beneath the roar of the river, another sound could be heard. Three short knocks from inside the darkness, followed by one long knock.
The three of them fell silent.
Senja looked at the radio in his hand, then toward the passage that did not appear on the map.
“No one sent that code,” Oscar said.
The river continued flowing into the darkness.
And from beyond the passage, something knocked again.