In January, Gill returned to the Nakanai, with 11 adventurers from the U.K., France, and the United States, on a two-month expedition to plumb one of the island's largest dolines, a half-mile-wide bowl called Ora.
The team's goal: To push deep into the cave at the bottom of Ora, map its enormous chambers, and follow the river boring through it—to the very end if possible.
"It's very, very remote," says Gill. "The terrain is so difﬁcult. You can't hike in a straight line, and it's totally unexplored. Even the local people don't go up there. There's nothing there for them."
From Port Moresby, capital of Papua New Guinea, the men traveled by plane and boat to Matong, a shore camp for loggers on New Britain. Then lumber trucks hauled them toanother camp, where the roads disappeared. A helicopter dropped them at a small settlement inhabited by a hundred members of the Kolpeople and two families of missionaries from the U.S. and Australia.
At ﬁrst, villagers suspected the outsiders were gold hunters. A few even pulled team members aside to show off the yellow lumps they'd found. "We'd just say, 'Oh yeah, fool's gold,'" says Dave Nixon, 38. "It's hard to explain that gold deposits don't occur in limestone."
The community soon warmed, and most villagers agreed to work as porters hauling supplies to base camp, a three-hour trek to a ridge overlooking the Ora Doline. Then the rain began, weeks of it, transforming the forest into a gleaming, mud-slick obstacle course.
At the bottom of the doline, the explorers followed the river into one side of the cave, then the other, hugging the narrow riverbanks underground, the water rumbling like a freight train. Often the banks disappeared, forcing the men to cross the river using ropes—a dangerous traverse where one caver would swim across, water boiling over him, to ﬁx a line for the others.
Jean-Paul Sounier volunteered for most of the swimming. Sounier, 55, has been caving for 40 years and made ﬁve previous pilgrimages to caves below the Nakanai.
"You can't afford an accident," he says. "It's not like home where if you have an injury, a rescue team will be quick to get you out." On New Britain, there was no rescue team.
Ora's upstream cave eventually opened into a massive cathedral, where a vaulted ceiling soared more than a hundred feet above a deep, turquoise lake. The downstream cave dead-ended after a third of a mile in a rock-ﬁlled sump where the river drained back into the earth.