The veteran actor, who is a longtime environmental campaigner, narrates a new film called National Parks Adventure, which is to be shown in IMAX cinemas across the U.S. to promote the state's natural wonders.

The film has been made in conjunction with Brand USA, an organisation which promotes U.S. tourism, and Oscar-nominated director Greg MACGillivray admits he was thrilled to bring the movie legend onboard.

He says, "I can't think of a more perfect narrator for National Parks Adventure than Robert Redford, whose passion for the outdoors and environmental interests as well as his distinctive voice and charisma, makes him the ideal storyteller for our film... Our hope is that National Parks Adventure will encourage our audiences to discover the beauty and sanctuary of these American treasures."