Veteran actors Robert Redford and Nick Nolte play an odd, old couple in the comedy “A Walk in the Woods.” The movie is amiable, if shallow, entertainment, until it falls off a cliff. Fortunately, the plunge doesn’t come until many miles into the story.

Road pictures — stories about travelers, often in cars but also trains, planes and boats — are nothing new. “A Walk in the Woods” is a trail picture. The two old-timers hike on the 2,185-mile-long Appalachian Trail.

Redford, 79, and Nolte, 74, play men who grew up in the same town. Following a youthful trek through Europe together, their lives took vastly different paths. Redford’s Bill Bryson is a noted travel writer. Nolte’s Stephen Katz is a recovering alcoholic and chronic philanderer.

Redford’s and Nolte’s characters are in the winter of their lives. In fact, “A Walk in the Woods” opens with a drive to the funeral home. When Redford and his wife, played by Emma Thompson, pay their respects to the widow, the celebrated writer chooses his words poorly.

Redford plays Bryson the wisecracker early on. Other than his wife and family, he has little interest in the human race.

“Talk to people,” Bryson’s wife admonishes him. “It’s good for you.”

“I don’t like talking to people,” Bryson replies.

Bryson’s wife, Catherine, seriously objects to her husband’s harebrained idea about walking the Appalachian Trail.

As Catherine, Thompson is a great actress with few scenes. She almost brings genuine poignancy to the film but, staying close to surface as the film uniformly does, Thompson just misses getting there. That’s a letdown.

Despite Bryson’s nonetheless sturdy relationship with his wife, “A Walk in the Woods” is all about his and Katz’s extended reunion on the trail.

When Nolte’s semi-incorrigible Katz enters the picture, Redford’s Bryson becomes straight man. Katz fumbles around. Unfiltered in speech and never considering the consequences, he says things in front of Bryson’s family that make his old friend squirm.

Katz is also in no condition to walk the trail. His lack of suitability for hiking hundreds of miles provides more comedy, including sight gags that are expected but still amusing.

“A Walk in the Woods” probably wasn’t intended to be Nolte’s show but that’s what it is. Next to Redford’s even-keeled to point of bland Bryson, Katz is a big, colorful guy, elderly but still capable of scene-stealing mischief.

Bryson and Katz meet some characters along their trek. Mary Steenburgen plays the inn proprietress who expresses romantic interest in Bryson. Meanwhile, Katz steals the show again with a brief, potentially disastrous encounter with another local woman.

A fellow hiker played by Kristen Schaal comes along, too. It’s a toss-up as to who she annoys more: Katz and Bryson or the audience?

Working with a slight script, Redford and Nolte keep “A Walk in the Woods” rolling longer than it deserves. But when they do reach the end of the trail, the show really is over, out of sight, out of mind, soon to be forgotten.