“You’re crazy,” I said. “You’re going up there in the pitch dark, with all those snakes, in the rain, wading in mud up to your balls, climbing that hill with a ton of gear on your back in a suitcase? You’re going to get yourself killed.”

He grunted and hiked off into the dark, his headlamp bobbing around before winking out entirely. As I hunkered down in my tent, listening to the rain, I was damned glad I was just a writer.

The rain stopped in the night and—finally—the morning of February 24 dawned beautifully, with fresh sunlight skimming the treetops. Some of the Honduran soldiers said they had seen petroglyphs downstream, where the river entered the notch on its way out of the valley. An expedition was organized to investigate. Chris Fisher and his crew decided to use the good weather to continue mapping the site, while Juan Carlos hoped to finish up his lidar scan of the cache. Steve and Bill Benenson joined our group heading downriver, along with Alicia and Oscar.

The weather was glorious. I washed my muddy, mildewed clothes in the river and put them back on, then stood on the riverbank in the warm sunlight, holding my arms out and turning about in a hopeless effort to dry my clothes. After so many nights and days of rain, even after laundering they smelled like they were rotting.

The AStar flew our group from our LZ to the Honduran LZ downstream at the river junction. A second group of Honduran soldiers had set up a camp at the junction, with tarps and palm fronds erected for tents, floored with cut bamboo. This was the only landing zone for the Honduran Bell helicopter, and these soldiers helped ferry supplies in and out and served as a backup to the group upstream. A side of deer ribs and two haunches were smoking over a fire, the rule against hunting having not yet been instituted.

We set off hiking downriver, Steve hobbling along, wading in the water with his walking pole, wearing a Tilley hat. The trip down this magical river was one of the most beautiful and memorable journeys of my life. We traveled mostly by wading in the stream, avoiding as much as possible the dense embankments, which we knew were a favorite snake habitat. (Venomous snakes are easier to see and less common in the water.) Snowy cumulus drifted across a clean blue sky. The area where the two rivers came together opened into a broad grassy field, and for the first time we could look around and actually see the shape of the land. The encircling ridge formed an arc in front of us, covered with trees; the conjoined river made a sharp right turn, running along the foot of the ridge, and then an abrupt left, cutting into the mountains and rushing through a ravine. For the first time, too, we could see the rainforest trees from top to bottom. Inside the rainforest, you can’t see the treetops or get a sense of what the trees look like and how tall they are.

After crossing the field, we waded into the river and hiked downstream. A tree had fallen across the river, with a tangle of limbs in and out of the water. The trunk was streaming with excitable, noxious red ants, which were using the tree as a bridge. We carefully wormed our way through its network of branches with the utmost care so as not to disturb them. We were lucky no one had been showered by these ants so far, which would require an evacuation and perhaps even a trip to the hospital. The river made a broad turn against the encircling ridge, running along a steep rocky slope thick with jungle trees that leaned over the river, dropping curtains of vines and aerial roots that trailed in the water, swaying in the current. The water was crystal clear until we stirred up the bottom, when it blossomed opaque with clouds of auburn silt. In some areas the river narrowed and became too strong and deep for wading; we were forced up on the embankment, where we followed the Honduran soldiers as they macheted a path for us, expertly flicking their machetes left and right, the blades going ping, snick, tang, snap—each species of plant making a different sound as it was cut.

As usual, we couldn’t see where we were putting our feet, and the fear of snakes was never far from our minds. And we did see one: a beautiful coral snake, banded in bright colors of red, yellow, and black, slithering through the grass. This snake has a bite that injects a potent neurotoxin, but unlike the fer-de-lance it is timid and reluctant to strike.

A few times we had to cross the river through rapids; there the soldiers formed a human bridge by linking arms in the water, while we waded through the current hanging on to them for dear life. As we reached the gap, we saw the first evidence of historic human occupation in the valley—a tattered cluster of wild banana trees. Banana trees were not native; originally from Asia, they had been brought to Central America by the Spanish. This was the only sign we ever saw of post-Conquest habitation in the valley.

We neared the gap: two forested slopes meeting in a V notch. The river took a ninety-degree turn at a place of heartbreaking loveliness, with thick stands of flowers giving way to a lush meadow and a beach. The river flowed in a singing curve over round stones and spilled in a waterfall over a ridge of basalt. In the shallows along the stream edge grew fat, blood-red aquatic flowers.

From the turn the river ran in a line as straight as a highway through the gap, faster and deeper, tumbling over rocks and fallen trees, sweeping around sandbars, dappled in sunlight. Rainforest giants leaned over the river from either side, forming a great cave echoing with the calls of macaws, frogs, and insects. The cloying smell of the jungle yielded to a clean scent of water.

Most of the people in our group halted at the opening to the ravine. Steve stretched out on a flat rock at the edge of the river, drying himself in the rare sunlight, not wanting to risk his bad leg by going on. Oscar cut some big leaves and laid them on the ground, making a bed, on which he took a nap. I decided to continue downstream looking for the petroglyphs, along with Bill Benenson, three soldiers, and the video crew.