In covering the expedition for National Geographic, I was partnering with the well-known photographer Dave Yoder. Yoder was a broad-shouldered, red-faced, gruff perfectionist who had come straight to Honduras from an assignment photographing Pope Francis in the Vatican. “I’ve never been so totally dislocated in my life,” he said on arriving in the jungle. On that assignment he had taken a candid picture of Pope Francis standing alone in the Sistine Chapel, which he shared with us on his iPad, expressing his hope it might become the magazine’s cover. It was an evocative and visually stunning photograph, and it did indeed make the cover of National Geographic’s August 2015 issue. He was bringing into the jungle three Canon cameras, two computers, and a suitcase of hard drives. Unlike many other photographers I’d worked with, he refused to set up a shot, ask someone to pose, or arrange a redo; he was a purist. As he worked, he never said a word; he remained a silent, scowling figure hovering in the background (or foreground, or in your face), his camera clicking almost continuously. In the rare times he did not have a camera, he became notorious for his dry, ironic quips. Over the course of the expedition he would take tens of thousands of photographs.

The team gathered at the Marriott Hotel in Tegucigalpa. Late in the afternoon, we convened with Honduran officials and military officers to discuss the expedition’s logistics. In the intervening years, Bruce Heinicke had died; long gone were the days of bribes, under-the-table deals, and implied threats of violence. The expedition had hired a team of less colorful but equally effective coordinators to make sure everything went as planned.

Chris Fisher had prepared huge lidar maps of both T1 and T3. These maps were a far cry from those first grayscale images we had seen on Sartori’s computer. The data had been carefully massaged and tweaked, realistic color had been added, and the images were now printed on paper charts in unprecedented detail. Electronic versions were set up to match an online “data dictionary” that would allow Chris to immediately mark and record on the electronic maps any feature he found in the jungle.

Steve Elkins unrolled the maps on the conference table, one showing T1, and the other T3. T1 was the primary objective, but Elkins hoped a quick ground survey of T3 might also be possible.

The first step was getting into T1 by helicopter. This was not a simple matter. The expedition had brought down a small Airbus AStar helicopter, and the Honduran Air Force also agreed to furnish a Bell 412SP helicopter and the soldiers who would accompany it. We needed to identify potential helicopter landing zones in T1 and figure out how to clear them of trees and other vegetation.

The Honduran military contingent was commanded by Lt. Col. Willy Joe Oseguera Rodas, a quiet, low-keyed man in casual military fatigues. He was a well-known figure in recent Honduran history—the military officer to personally handcuff deposed president Zelaya during the 2009 coup.

Oseguera opened the discussion by explaining that the air force had closely examined the terrain and felt that the only safe landing zone for their Bell 412 was twenty kilometers away—outside the valley. Elkins disagreed. Twenty kilometers in the Mosquitia mountains might as well be a thousand miles; an overland journey of that length would take a week or more, even for seasoned jungle troops.

“This,” Elkins said, gesturing at the huge map, “is the T1 valley. There’s only one way in—through this gap. Where the two rivers split, there’s an area of no trees. This would be an easy area to land, but it would require the clearing of two to three meters of brush.” He pointed to an area a few miles to the north, just below the city. “And there’s another possible landing place next to the ruins. But the trees might be too close together.”

The military men wanted to know exactly how tight these two landing zones were.

Elkins brought out his laptop and booted up the three-dimensional point cloud of the landing zone, which, remarkably, can be rotated and sectioned in any way. Chris and Juan Carlos had already prepared for him digital cross sections of several potential landing zones, which showed the trees, the height of the brush, and the ground level, exactly as if the landscape had been sliced vertically with a knife. Steve had also hired a plane for Juan Carlos to fly over the potential landing zones late in the fall of 2014, to see if there were any noticeable terrain changes and to take good, visible-light photographs and video. All this preparation paid off. It appeared that the river junction LZ might be just large enough for the Bell, and that a smaller LZ might possibly be cleared on the bank of the stream below the ruins, broad enough to insert the AStar.

All this remained theoretical until it could be confirmed in a visual reconnaissance overflight of the valley, planned for February 16, in two days’ time.

Lt. Col. Oseguera explained that once we had scouted out our location, the Honduran military would deploy sixteen soldiers in the valley, who would camp next to our base camp and provide security. These were Special Forces TESON soldiers, many of whom were indigenous Pech, Tawahka, Garifuna, and Miskito people from eastern Honduras. “The soldiers are self-sufficient,” Oseguera said. “They camp on their own. They are very old-school and live like Indians.” The soldiers, he said, would be providing security against possible narcotraffickers, criminals, or others who might be hiding in the forest, although that seemed unlikely, given the remoteness of the valley. They would, more importantly, be taking part in a military exercise called Operación Bosque, “Operation Forest,” to train them on how to protect the rainforest and its archaeological treasures.