Text by Katia Hetter; Video by Channon Hodge, CNN and Alfredo Alcantara CNN

(CNN) -- Pete McBride is worried about the Grand Canyon, so he decided to hike it.

All of it.

A few years ago, the adventure filmmaker, photographer and writer filmed the path of the Colorado River and was amazed to see that the river doesn't reach the ocean anymore.

The river "flooded the sea for six million years, and it stopped two decades ago," says McBride, who has traveled to 75 countries for a host of publications and projects over 20 years.

The trip "made me shift my focus, so now I do a lot of photography around conservation, around fresh water and around public lands."

Having hiked Mount Everest and documented nature in Antarctica, he didn't think the Grand Canyon needed his images to survive.

"I figured the Grand Canyon was one of the most protected pieces of landscape on the planet, so it didn't require another photographer to go photograph there."

Learning about current threats to the canyon changed his mind.

One of the seven natural wonders

One of the seven natural wonders of the world and a UNESCO World Heritage Site, the Grand Canyon is one of the most photographed landscapes in the world.

The Grand Canyon is about five or six million years old, but rocks at the canyon bottom date back about 2 billion years. Human artifacts have been found dating back nearly 12,000 years to the Paleo-Indian period, and it's been continuously occupied into the present day.

The land now known as Grand Canyon National Park, which celebrates its centennial anniversary in February, was first protected by the US government in 1893. When Congress resisted US President Theodore Roosevelt's effort to make it a national park, which required Congressional approval, he protected it as a national monument in 1908, which he could do without their help. It became Grand Canyon National Park on February 26, 1919.

"In the Grand Canyon, Arizona has a natural wonder which is in kind absolutely unparalleled throughout the rest of the world," said Roosevelt at the time. "I hope you will not have a building of any kind, not a summer cottage, a hotel or anything else, to mar the wonderful grandeur, the sublimity, the great loneliness and beauty of the canyon. Leave it as it is. You cannot improve on it."

Given that illustrious history, McBride was surprised to hear from people working inside and around Grand Canyon National Park that the canyon faces multiple threats.

They come from increased helicopter flights, a proposed tram to the canyon floor, proposed tourist developments and possible uranium drilling. (The threat of uranium isn't a hypothetical issue: Three buckets of uranium ore were stored at the park museum for nearly two decades, according to a park employee who went public in February. Federal officials are investigating his report.)

While some of the developers who want to make money off the park aren't from the area, some are Native American tribes who have watched others profit for decades.

A park under threat of development

Most visitors spend only a few minutes at the South Rim, experiencing just that famous view of Grand Canyon National Park, unaware of the canyon's role as home to ancient peoples, animals and plant life or the threats and economic pressures placed on it.

So McBride decided to hike the length of the canyon, a 750-mile journey (give or take a few miles).

There wasn't any thru-trail for him to follow. And the hike would include an elevation gain and loss of around 100,000 vertical feet, unstable rock and temperatures fluctuating from 8 degrees to 116 degrees Fahrenheit.

"I don't know why I got the idea to walk it," since there's no trail for much of the distance, he says. "I figured it'd be challenging, but I've done a lot in the back country and wilderness and I figured it couldn't be that hard. And oh, how wrong I was."

When McBride and his friend, writer Kevin Fedarko, first started planning their hike, they convinced experienced Grand Canyon hiker Rich Rudow to let them join his September 2015 hike.

It didn't go well.

Loaded up with way too much camera gear and not prepared for the impact of the extreme heat on their bodies, the canyon made them sick and disoriented, forcing them out on their sixth day, as Fedarko later wrote in National Geographic.

Back in Flagstaff, Arizona, McBride was diagnosed with hyponatremia, a heat-induced imbalance of salts and minerals, which could have killed him.

There would be no thru-hike.

In fact, McBride and Fedarko thought about quitting as they got medical attention and recovered from their first attempt. But the local hiking community and Native American conservationists convinced them to complete the trip in order to draw attention to the magnificent natural wonder.

Hiking in two-week stints

During five weeks in October, they planned a hiking trip that involved hiking the canyon in two- to three-week stints starting in November 2015 going through March 2016, often bringing more experienced Grand Canyon hikers along, traveling about 15 miles per day and 150-200 miles per trip, completing about 600 miles before summer.

They skipped hiking during the deadly hot summer months -- but still photographed the park -- and finished up their last two-week stint in late October of 2016.

"There's no trail for 70 to 80 percent of it, so you have to find your way and you have to learn how to find water. You have to make sure you don't get pinned up on a cliff, just kinda figure out how to stay alive," McBride said. "it's a great lesson in humility and self-sufficiency and getting back in tune with our natural world."

He carried just one camera, a Sony A7 with a wide angle lens 16-35, to shoot the video that became "Into the Grand Canyon," a movie airing on National Geographic and streaming on NationalGeographic.com, and the pictures that became his book, "The Grand Canyon: Between River and Rim."

McBride went through eight pairs of shoes over 13 months, hiked through four sprained ankles, two broken fingers, that case of hyponatremia, lost two girlfriends and even threw his heart out of rhythm, requiring heart surgery.

The lessons he learned, the wisdom he gained, the humility he earned -- all of that, plus a careful selection of his images, were more than enough to fill his book.

Here are some of his discoveries on the journey, in his own words and adapted from his book:

It can be viewed from space

"Despite my fatigue, I often lay awake at night: sometimes too wired and worried about finding water and sometimes too spellbound by the spray of stars above us. Kevin (Fedarko) describes this celestial sweep as a second river -- one that mirrors the main Colorado below us.

"Being inside the only canyon on the planet that can be seen from space makes you feel miniscule. And when you stare skyward, you realize one of this landscape's unspoken marvels is the clarity of its night sky -- one of the few landscapes in America without a blanket of light pollution. I lose myself in the space above and the idea that Mother Nature is still queen in some parts.

"As I doze, I overhear Kevin taking audio notes (easier than writing when he is tired), remarkably 100 yards from me. It is so quiet I think he is five feet away. He describes these moments 'below the river of stars' as if 'the canyon is holding us in the palm of its hand.'"

A silence so profound

"When you get beyond the roar of the river inside the canyon, the silence is so profound and so ancient that it escapes description. At times it makes my ears ring because I'm trying to listen so hard to something that isn't there. At other times the void of noise is so profound I wonder if it belongs to another world -- a world we have long forgotten.

"In the evenings or early mornings, Kevin and I can converse in relaxed, tired voices even though we are the length of a football field apart.

"The same occurs when we hike, but if a single rib of rock separates us, we can't hear each other holler at the top of our lungs, as if, at times, our voices can't pierce the blanket of quiet that envelops us."

The unfiltered night sky

"The clarity of Kevin's 'river of stars' is hemmed on the edges by the distant glow of Las Vegas and St. George, Utah. Otherwise, looking across the sweep of erosion, rock, and time, there is no sign of civilization before us. Of course, we do see jets blinking above, mostly headed to Los Angeles, but they die down after midnight.

"It's so silent (that) you can be laying in the morning, and you can hear just the distant brush of the bat wings as they're going out and looking for bugs, and you could hear the little clatter of sheep hooves on a rock layer that might be 1,000 feet below you.

"We just don't have a silence that's that deep ... it made me realize just how magical that is and what a noisy world we live in.

"I think that was part of the magic where it changed me to a degree, and I now am very aware of noise and silence. It's not silence without sounds. It's a silence without the chaotic noise of human sounds. It's a silence layered with these rich wildlife sounds that we've forgotten or our senses are not used to hearing."

You, too, can go deeper into the canyon

While many visitors only visit the South Rim or take a short (and noisy) helicopter ride to view the canyon, McBride says there's a better way to appreciate this magnificent national park without risking one's life on a year-long adventure.

Pack a hat, good hiking shoes and lots of water and choose to spend the day at the canyon beyond a few minutes at the South Rim. "Experience it away from vehicles. You can do that in a variety of ways."

Visitors can hike into the canyon, just remembering that the hike back up is twice as hard. Visitors can also ride a mule down into the canyon and back up, or ride one way and hike the other way.

Bicycle lovers can rent bicycles and ride the bike path along the South Rim or mountain bike on the trail on the North Rim (open seasonally). Guests using wheelchairs will find some wheelchair-accessible trails, including the Trail of Time and parts of the Rim Trail.

Hardier types can hike two-thirds of the way into the canyon (with all of your gear) and camp at Indian Garden Campground, where there is drinking water. There are also rafting trips for every skill level.

Listen to the sounds

If you take some time to listen to the sounds of the canyon, quietly, McBride says it may change you.

"The silence of this natural wonder starkly contrasts with the noise we make everywhere else, even as the canyon invites us to carry some of that silence within ourselves as we return to the world beyond the rims," writes McBride.

"As I wonder if any of my images have captured that, I find myself pondering an even deeper question: Is it possible that this journey by foot, along with the photographic record that it has yielded, might help illuminate and underscore what we all share -- as well as what we all risk losing -- if we fail to protect this vast abyss by foregoing the urge to transform its beauty into cash and simply leaving it as it is?

"While the answer to that question is for others to decide, I do know one thing. After spending so many months drenched in the silence and magic of the seventh natural wonder of the world, I know there is only one place that looks and sounds like this."