"I think it's our best film," Ken Burns says, sitting with co-producer and writer Dayton Duncan in front of a roaring fire at Yellowstone's Old Faithful Snow Lodge in January. The 56-year-old filmmaker is here on a "victory lap" to thank people who helped on the project; Duncan also wanted to bring Burns in winter to see Yellowstone empty, as close as possible to its original state. They went wolf spotting in the morning (Burns had never seen a wolf in the wild), and the expedition did not disappoint. We'd had a rare "three-dog day," seeing all three of the park's canine species: coyote, fox, and wolf. "We used to kill them," Burns says. "Their reintroduction is a big story in our film." He pops open a tiny bottle of champagne and offers a toast: "To Yellowstone."

Burns is toasting the park as the centerpiece of his most ambitious project, 'The National Parks: America's Best Idea,' a six-part documentary that includes all the signature Burns elements – sepia-tinted photos, camera pans, characters voiced by famous actors like Tom Hanks and John Lithgow – but also utilizes extensive original footage. Burns filmed in 53 parks, and even rented helicopters for aerial shots – making this the most expensive Ken Burns production yet (possibly ever, considering the main underwriters of the $15 million budget are Bank of America and GM). The entire project took 10 years.

"We don't do things quickly, and we don't make short documentary films," says Duncan, who explains that their aim was to tell the history of the parks' creation and the people behind it, not to produce a nature film. But that's a bit misleading, since the film opens with 14 straight minutes of epic landscapes and returns frequently to footage of wildlife. "A herd of bison would come by and we'd spend an hour shooting them," Duncan admits.

Although such footage, particularly in episode one, may test viewers' patience, the narrative picks up and is carried by men like John Muir, whom Burns calls "the ghost who haunts the film"; Teddy Roosevelt, who left his security detail behind to spend a week observing Yellowstone's animals; and Truman Everts, a nearsighted 54-year-old who in 1870 lost his expedition and spent 37 days wandering the wilderness with no supplies, yet survived. "The first tourist," Duncan jokes.

Burns's series arrives at a critical moment for the parks, which have been starved for funds and have the rough edges to prove it. The U.S. National Park Service has drawn up a $3 billion renovation wish list for its 2016 Centennial. "Given the current situation, that's a drop in the bucket," Burns says. He's vowed to do his part, putting together a reel for President Obama highlighting the "important activist presidents" and pointing out that the parks actually thrived after the Great Depression. At the same time, if more visitors come to already overcrowded parks, rangers will know who to blame. Shortly after The Civil War first aired, Burns was touring a battlefield with that park's superintendent when the man picked up a candy wrapper. "This is your fault," he said, only half joking.

Moments to Watch for in 'The National Parks: America's Best Idea'

EPISODE 2: "The Last Refuge," 1890–1915
Hearing that buffalo are nearly extinct, an alarmed 24-year-old Teddy Roosevelt rushes west to the Badlands – to shoot one, cut off its head, and send it home to be mounted on his wall. Later, as president, on a visit to Yellowstone he kills and stuffs a mouse.

EPISODE 3: "The Empire of Grandeur," 1915–1919
Not long before his death, legendary explorer Bradford Washburn describes Mount McKinley: "There's something distant and special about that mountain. Well, it's bigger than hell. And it's colder than hell on top. They said it was cold as the heart of an elderly whore."

EPISODE 5: "Great Nature," 1933–1945
After secretly buying up tens of thousands of acres in the Grand Tetons, John D. Rockefeller Jr. donates them for a national park – and ignites a firestorm of outrage. The governor of Wyoming threatens to use state police to keep out any national park officials.

EPISODE 6: "The Morning of Creation," 1946–1980
President Jimmy Carter bypasses a stalling Congress and invokes the Antiquities Act, creating 17 national monuments that set aside 56 million acres of Alaska for the National Park Service. Alaskans call Carter a tyrant for stealing their land and burn him in effigy.