When archaeologists ventured into a thick Honduran rainforest in 2015, they were searching in an unexplored valley for the remnants of a long-lost city. Legend had it that an ancient metropolis was buried under centuries worth of jungle growth.

Deep in the forest, with the help of new technologies, scientists discovered the untouched ruins of a vanished culture.

“Usually an archaeological discovery takes a long time. There’s a lot of digging, you sit around doing nothing," says Douglas Preston, who went along on the expedition. “In this case, they flew over the valley with this million-dollar LIDAR machine in the plane. In three days they mapped the valley; the next day they had an image of the ground with the trees removed, and the reaction of the scientists was something I’d never seen before."

Preston has detailed the experience in a new book, "The Lost City of the Monkey God: A True Story.”

The archaeologists Preston followed had the advantage of detailed survey maps to guide them to precise locations. Three years earlier, scientists had deployed advanced LIDAR (Light Imaging, Detection, And Ranging) technology to peer through the rainforest canopy to reveal a sprawling ancient metropolis.

Preston says many of the scientists on the mapping expedition were skeptical there would be anything in this remote valley, and initially felt it was a crazy, obsessive search. Seeking the lost city, also called "the White City," is a fabled search adventurers have taken on since conquistador times.

“But when we saw these images," Preston says, "you didn’t have to be an archaeologist to see a pyramid, plazas, mounds, terracing — it was incredible and stretching for several miles along this valley.”

The jungle at dawn, seen from the banks of the unknown river flowing through the valley, 2015. Credit: Douglas Preston

The 2015 ground expedition was mounted in cooperation with Honduras. It was a treacherous undertaking. The river valley where the team headed is near a corridor used by cocaine smugglers. There were mosquitos (and malaria) to contend with, not to mention jaguars and deadly snakes. In his book, Preston writes about one of the team’s first moments of discovery in the jungle:

“We had to win every foot by machete, our blades marked with stripes of pink Day-Glo tape so we could avoid one another’s slashing strokes cutting through the vegetation. Even so, we had some close calls.

"On the third day, we ... stumbled over a cache of objects at the base of the pyramid that would prove to be of singular importance. As we were strolling past a leafy hollow in the drenching rain, a team member spied, peeking from the leaves, the carved head of a snarling jaguar. A shout went up and everyone crowded in to see. Just poking out of the ground were the tops of dozens of stone sculptures. The objects took shape in the forest twilight: vessels with carved rims; thrones decorated with the heads of half-animal, half-human deities; bowls; and effigies. They were all almost entirely buried, with only the tops visible, like stone icebergs.

"I can recall the very moment when I first saw that jaguar head coming out of the ground. Gleaming with rain, it rose up snarling, as if struggling to escape the earth. It was an image that spoke directly across the centuries — forging an immediate, emotional connection to these vanished people. What had been theoretical became real: this spirited image had been created by people who were confident, accomplished, and formidable. Standing in the gloom among the ancient mounds, I could almost feel the presence of the invisible dead."

The jaguar head as it first appeared emerging from the ground. David Yoder photographed the artifacts using a special “light-painting” photographic technique. Credit: Dave Yoder/ National Geographic Magazine

So who were the people who lived in this grand city? What was their fate after Christopher Columbus and Europeans arrived to the New World? And how did this city disappear back in the 16th century?

The answers are all in Preston's book.

Mystery surrounds The Lost City of the Monkey God. Read all about it in Douglas Preston's new book, available for pre-order. pic.twitter.com/k1KtVsZfR1 — Grand Central Pub (@GrandCentralPub) December 16, 2016

Editor's note: This story has been updated from an earlier version.