The plane’s propeller roared furiously in my ears.

A brown river twisted far below, following the path it’d been cutting for a million years. The dense jungle strangled it hard, but the river seemed relaxed, barely a ripple on its surface. The pilot’s voice crackled through the cabin, “preparing to land at Gunung Mulu National Park.”

The legendary Gunung Mulu National Park. There are few places like it in the world. Featured on the BBC’s Planet Earth, it’s host to one of nature’s most spectacular performances. Every day, three million bats fly from its caves to feast on insects. If I was lucky, I’d see this exodus.

Gunung Mulu is so isolated that it has no road access — the way in is by plane. Upon landing, I exited the aircraft, walking straight off the runway and onto the street that ran parallel. A handful of basic guesthouses lined the road. Robert, an owner of the guesthouse I stayed at, surprised me by saying that he’d studied in New Zealand.

Over the next four days I explored the park, marveling at its biodiversity and intricate ecosystems. This started with a walk through the jungle canopy, following wooden bridges strapped to the trunks of the tallest trees. I was a guest in a forbidden kingdom.

Although there wasn’t much wildlife on display, it was fascinating just watching the plants’ battle for survival. The adaptations of the creepers and the lianas; the epiphytes growing on the ancient branches. Meanwhile, plants lay dormant on the jungle floor, waiting for the chance to burst skywards once a tall tree fell.

And then there was the smorgasbord of arachnids and insects. Delicate butterflies, bumbling spiders, translucent ants and furry caterpillars. Each one adapted to life in Gunung Mulu.

But it was the caves that had drawn me to Gunung Mulu. Later that day I visited Deer Cave, the largest cave passage in the world. I approached the cave through the dense jungle, following a slippery path. The trees parted and a massive limestone wall shot up from the valley floor. In its centre was the Deer Cave entrance, gaping like a sea monster’s maw.

The cave was 170 metres high in places with a ceiling that was literally alive. Three million bats call it home, a writhing black mass that clings to the rock. Their squeaking echoed in the cave, and I followed some sage advice — don’t look up with your mouth open. The cave floor was carpeted in guano, a deep sea of bat shit.

I exited the cave into a proper tropical rainstorm, thick pellets of water shooting from the sky. I wanted to stay in the cave and presumably so did the bats. They didn’t leave to feed, much to my disappointment.

The next morning I went to the Clearwater Cave. With Robert as a guide, our group traveled by longboat, which carved a path through the murky river. We stopped at Batu Bungan, the depressing village of the semi-nomadic Penan people who’d once lived in the jungle. They’d been displaced after interfering with the government’s attempts to illegally log the rainforest.

Robert explained how the government had built a settlement for the Penan, but that it kept burning down. This was a mystery worthy of Sherlock Holmes.

We walked through the village, which looked more like a slum, ending up at a small market. Glum old women were selling trinkets to idiotic visitors from Kuala Lumpur. They looked like they hated us, which was totally justified. After all, it was our modern lifestyle that created the demand for resources that had driven them from their traditional homelands.

I raised this with one of the young backpackers in the group. “Whatever,” she replied, “this happens everywhere.” I didn’t speak to her again.

We continued downriver, stopping at Wind Cave. A breeze blew through it, whistling softly. Stalagmites rose from the floor in imperious columns, forming a forest that appeared to hold up the ceiling.

But the best came last — Clearwater Cave. While Deer Cave was massive, Clearwater won with its sheer beauty. It captured the imagination with the way it flowed, dropped, rose and curved. The humidity inside was cloying, so afterwards I swam in the river that flowed from the cave. A small bat flitted across the surface, trying to catch fish in the cool water.

Tomorrow I’d be leaving Gunung Mulu yet I still hadn’t seen the bat exodus from Deer Cave. So that evening I returned for one last try, fearful that it would rain again and ruin everything. 

To my despair, it did rain, but the bats were clearly hungry. A small trickle left the cave, looking like a swarm of bees. This soon turned into a river of bats, braving the hammering rain. They surged in a black cloud which writhed against the grey sky.

To me on the ground this was a beautiful spectacle; but for the bats it was a deadly warzone. Their rhythmic movement was an attempt to dodge the preying hawks that lingered outside the cave, diving into the morass and causing chaos with their murderous talons. After a full hour the river became a stream and then nothing, three million bats had left to feed in the night sky.

I walked back through the jungle alone, my torch the only light. The din of a billion insects surrounded me. I tried to suppress thoughts of the supernatural horrors lurking just out of sight, before stumbling upon a real nightmare.

Inching along the path was a pair of giant stick insects, so vast that they had their own gravity. An unholy stench seemed to fill the air, pervading from their spiky carapace. But I was drawn to them in a way that defied their foulness.

The next afternoon I left Gunung Mulu, the tarmac becoming air below the plane’s wheels. The view from the windows was majestic, and I said goodbye to the brown river. But far too quickly the view became tragic, a scene of ecological genocide. The jungle receded, torn down and replaced by endless rows of palm trees. Their straight lines betrayed that this was not the work of mother nature — it was another palm plantation, the cause of so much deforestation in Borneo.

I thought about what I’d seen over the past days and was struck by the sadness of what had also been lost. Gunung Mulu, for all its wonders, was an increasingly rare oasis.