700 metres into an underwater cave beneath the Indonesian jungle, Rannva Joermundsson paused to catch her breath. Her equipment felt uncomfortable. A twinge of fear crept in. Her diving partner, Maria Bollerup, scrutinised Joermundsson’s body language. Verbal communication is impossible in the watery underworld, but the pair’s twin-like bond told Bollerup something was wrong. They aborted the dive.

Like astronauts, cave divers can’t ignore slight hitches in instruments or gut feelings. Lives – not just objectives – are always at stake. But those decisions aren’t easy when there’s only one shot. Bollerup and Joermundsson’s mission was to collect samples – water and chunks of earth – from the heart of Laulawi, a subterranean cave system beneath the Indonesian island of Pulau Muna. But they were only one leg of an extreme relay, each elite team taking the baton where the last had reached its limits. Dry cavers had kicked it off, hacking entry points through the hot, humid jungle. An underwater push team laid navigational groundwork for others to collect samples, which scientists would test. Eventually, communicators would bring the findings to the public.

Together the teams raced to protect Laulawi from the encroaching threats of cement mining and water bottling efforts by establishing it as a Geopark. This would be the first step in ultimately applying to be a World Heritage Site through the United Nations Educational, Scientific and Cultural Organization, or UNESCO – a dream that started with a Frenchman on holiday.

In 2016, Robin Cuesta, a French scuba diving instructor, was searching for a holiday, for caves to explore, and for purpose. He wanted to apply his diving skills to conservation efforts. The Indonesian archipelago contains over 17,000 karst, or limestone-like, islands where caves should be prolific, but Cuesta’s initial search for diving sites yielded no results. Finally, he identified Buton Tengah, or Buteng, an extremely remote region on the island of Pulau Muna. “And I was lucky,” he said. “I found quite a lot.”

Cuesta’s holiday turned into a permanent stay. He was virtually the only foreigner on the island, but he integrated, building relationships with the village elders, and learned the local dialect. Cuesta set up a dive shop and continued his quest mapping the sprawling underground labyrinths of the island. In 2018, he found an entrance to an aquifer called Laulawi. He knew it would be big – a water pump clearly drew drinking water from it – but he pushed it to the back of his mind. “I kept this cave kind of on the side,” he said, thinking, “we’ll explore it later.”

In 2020, Bollerup and her husband, Rasmus Dysted, a Danish technical dive instructor, visited Cuesta to do some exploring. It was the perfect moment to finally enter Laulawi’s waters. Divers map caves using reels of white nylon guideline. The trio pushed the caves until their guideline reels were completely empty. There was no end in sight. To fully explore this system, they would need a larger team, higher tech equipment, and many more reels. Laulawi is the only source of freshwater in Buteng. Despite having a vast and pristine freshwater source just metres beneath their feet, many inhabitants lack access to taps and rely on bottled water. Water scarcity is a real concern. Local leaders want to expand freshwater access – but responsibly.