A few steps ahead of me on the jungle trail, my Dayak friend and guide, Ham, suddenly stopped. "Careful, Luc, a snake!" he said. The rain had fogged my glasses, but I could still make out the big bluish black cobra he'd almost stepped on. A snakebite could have been deadly, since we didn't have any serum with us, and the closest clinic was two days behind us by foot, and another two days by boat. We stood in silence, listening to the patter of rain on the tropical forest as the cobra unfurled itself and disappeared into the bushes.
We were heading for Ilas Kenceng, the most beautiful and inaccessible of all the caves we'd discovered in Borneo. When we first saw it in 1998, we had only a few hours to study its mysterious rock art before we had to hike out, leaving us with many unanswered questions: Who made these images? When? And why? Now we were on our way back to look for more clues.
There were 35 of us in all on our French-Indonesian team, including archaeologists, cavers, guides, a film crew, canoe paddlers, porters, and a cook. We'd begun our expedition a month before on the coast of the Makassar Strait in East Kalimantan in the Indonesian part of Borneo. Pushing off into the chocolaty Bungalun River in ten heavily laden pirogues, we'd headed for a region where there are no roads or villages, only endless jungle and jagged limestone peaks. Our plan was to follow the Bungalun to its confluence with the Marang River, then continue north into the mountains, stopping along the way to investigate a string of caves with similar rock art.
Sitting on the duckboards of my precarious little boat, its gunwales inches above the waterline, I'd thought back to my first expedition here 17 years ago. A documentary filmmaker and magazine editor, I had set out on a 700-mile (1127 kilometers) trek from one end of Kalimantan to the other with a few caving friends. Halfway across the island, taking shelter under a rock, we found ancient charcoal drawings on the ceiling. When I returned to France, I was surprised to learn that no such rock art had ever been reported in Kalimantan.
I returned in 1992 with Jean-Michel Chazine, a French archaeologist and specialist in Oceanian prehistory. Two years later we discovered prehistoric paintings in East Kalimantan. In 1995 Pindi Setiawan, an Indonesian anthropologist, joined our team, and together, year after year, we found dozens of caves with paintings throughout the region, some with unique designs hinting at a mysterious forgotten people.
To reach our target caves this year, we followed the meandering river along the jagged peaks of the Marang Mountains. There we set up camp beside a clear spring, stringing hammocks between trees. For his dinner, our cook roasted six-inch-long (15.2 centimeters) scorpions, which he said were good for virility. The rest of us preferred rice. The wind kicked up just before dark, shaking leaves from the forest canopy, and a tropical storm pelted down. Once it had passed, the red ants swarmed in, their bite as painful as wasp stings. Jufri, a Bugi guide who always seemed to think of everything, drove them away by lighting just enough gasoline under our hammocks.
The next morning, back in our pirogues, we motored toward Gua Tewet, a cave named for one of our most experienced guides. For the past 40 years, Tewet had been searching caves in the region for edible birds' nests, a delicacy in great demand at Singapore and Hong Kong restaurants catering to wealthy Chinese. Several years ago he'd remembered the cave and told us about it.