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When Robert Redford was an 11-year-old boy, his mother took him to Yosemite National Park to reward him for getting over a mild case of polio. And that, the actor says in an exclusive trailer for National Parks Adventure, is when everything changed for him.

Redford recalls driving through a mile-long tunnel and emerging to find a beautiful landscape, one he immediately wanted to surround himself in. “I said, ‘Wait a minute. I don’t want to look at it,'” he says. “‘I want to be in it.’ I think that’s when my passion for nature and the environment began.”

Since that pivotal moment, Redford has been an outspoken environmental activist, donating his time and money to causes for over 40 years. Now, he’s honoring the National Park Service on their centennial by narrating National Parks Adventure, a Greg MacGillivray-directed IMAX film that explores over 30 national parks.

“There’s something about solace in those places, something almost spiritual in the power of these parks,” Redford says in the clip. Watch above to see a sneak peek of the film, which arrives in theaters Friday, Feb. 12.