Chris Fisher, the archaeologist, appeared, wearing a white straw cowboy hat that shone like a beacon in the gloom. “Hey, you guys, welcome!”

I looked around. “So… what do we do now?” Woody and the other two SAS men were busy arranging supplies.

“You need to find a place to string your hammock. Two trees, about this far apart. Let me show you.” I followed him through the trees to his campsite, where he had a green hammock set up, with a rainfly and mosquito netting. He was lashing together a small table from cut pieces of bamboo and had strung up a tarp to sit under in case it rained. It was a very good camp, efficient and well organized.

I walked fifty yards into the forest, hoping the distance would preserve my privacy after everyone else arrived. (In the jungle fifty yards is a long way.) I found a pleasant area with two small trees the right distance apart. Fisher loaned me his machete, helped me cut a small clearing, and showed me how to hang the hammock. As we worked, we heard a commotion in the treetops. A troop of spider monkeys had collected in the branches above, and they were unhappy. They screeched and hooted, coming down lower, hanging by their tails while shaking branches at us in a rage. After a good half hour of protest they settled down on a limb, chattering and staring down at me as if I were a freak of nature.

An hour later, Woody came by to check on my camp. He found my hammock job wanting and made some adjustments. He paused to watch the monkeys. “This is their tree,” he said, sniffing a couple of times. “Smell that? Monkey piss.”

But it was getting late and I didn’t want to go to the trouble of moving my camp. I was beyond the fringes of the group, and concerned that after dark I would need a good trail so as not to lose my way. I walked back to the LZ, clearing a better trail with the machete, losing my way several times, having to backtrack by following the cut plants. I found Juan Carlos in his newly set-up camp. Along with Chris we went down to the bank of the stream and stared across the river at the wall of trees. It mounted up, tier after tier, a barricade of green and brown, dotted with flowers and screeching birds. Beyond that, no more than two hundred yards away, began the edge of the lost city and the possible earthen pyramid we had seen on the lidar images. They were cloaked in rainforest, completely invisible. It was about five o’clock in the evening. A soft yellow sun spilled into the rainforest, breaking into rays and flecks of gold, scattering coins on the forest floor. A few fluffy clouds drifted past. The stream, about three feet deep and fifteen feet wide, was crystal clear, the limpid water burbling over a pebbled bed. All around us, the rainforest chattered with the calls of birds, frogs, and other animals, the sounds mingling together into a pleasing susurrus, punctuated by the call and response of two scarlet macaws, one in a nearby tree, the other distant and invisible. The temperature was seventy degrees, the air clear, fresh, and not humid, perfumed with the sweet smell of flowers and greenery.

“Have you noticed?” said Chris, holding up his hands and smiling. “There aren’t any insects.”

It was true. The fearful clouds of bloodsucking insects we had been warned about were nowhere to be seen.

As I looked around, I thought to myself that I had been right and this was not at all the scary place it had been made out to be; it felt instead like Eden. The sense of danger and unease that I had been carrying as an unconscious weight since Woody’s lecture subsided. The SAS team had, naturally, tried to prepare us for the worst, but they had overdone it.

As dusk fell, Woody invited us into his little bivouac area, where he had a tiny stove going with a pot of boiling water for tea and for hydrating our evening’s freeze-dried dinners. I opened a packet of chicken tetrazzini, poured in boiling water, and then, when it had absorbed the water, spooned it from the bag into my mouth. I washed it down with a cup of tea, and we stood around listening to Woody, Spud, and Sully tell stories of their adventures in the jungle.

Within minutes, night dropped like the shutting of a door—absolute blackness fell upon us. The sounds of the day morphed into something deeper and mysterious, with trills and scratchings and boomings and calls like the cries of the damned. Now the insects began to make their appearance, starting with the mosquitoes.

There was no fire. Woody lit a Coleman lantern that forced back the darkness a little, and we huddled in its pool of light in the great forest while large animals tramped, heard but unseen, in the jungle around us.

Woody said he had spent a large part of his life in jungles all over the world, from Asia and Africa to South and Central America. He said he had never been in one like this, so apparently untouched. As he was setting up camp, before we arrived, a quail came right up to him, pecking in the dirt. And a wild pig also wandered through, unconcerned by the presence of humans. The spider monkeys, he said, were another sign of an uninhabited area, as they normally flee at the first sight of humans, unless they are in a protected zone. He concluded, “I don’t think the animals here have ever seen people before.”

All three of the ex-SAS team were absurdly bundled up against the insects, covered from head to toe with insect-proof clothing, which included a hood and a head net.

“Is that really necessary?” I asked.

“I’ve had dengue fever twice,” Woody said, and launched into a shockingly graphic description of the disease, which had almost killed him the second time. It is called “breakbone fever,” he said, because it is so painful you feel like your bones are breaking.