Warning: If you and I are on a flight someday in the near future and I see you watching “The Lost City of Z” on a handheld device, I’m might snatch that thing out of your hands.

Fine. I won’t do that because I don’t want to star in a viral video titled, “Critic Snatches Thing Out of Hands of Person Watching ‘Lost City of Z’ on Three-Inch Screen,” but I can’t stress enough how much you’ll be missing if you don’t check out James Gray’s breathtaking and stunning epic on the biggest screen imaginable.

In the tradition of “Fitzcarraldo,” “The Emerald Forest” and “Apocalypse Now,” this is the type of adventure that transports you to a world so exotic and lush and mysterious and dangerous, it feels as if we’re on a different planet.

Charlie Hunnam (“Sons of Anarchy,” “Pacific Rim”) has the golden boy/leading-man looks of a young Robert Redford or Brad Pitt (an executive producer on this film who once considered playing the lead), but like the aforementioned, he also has genuine chops. Hunnam gives the best performance of his film career as Lt. Col. Percy Fawcett, who in the early 19th century became obsessed with finding proof of an ancient but advanced civilization deep in the Amazon.

As portrayed by Hunnam, the British explorer is a smart and forward-thinking visionary, a loyal friend and a loving family man — but he’s also self-promoting, self-righteous, ego-driven and forever concerned with restoring the reputation of the family name, which had fallen out of favor among the British upper crust.

When we meet Fawcett, he’s an undecorated military man who is devoted to his pregnant wife Nina (Sienna Miller, excellent) but also worried he’s running out of chances to boost his career and make his mark on the world. When the Royal Geographical Society of London agrees to fund a two-year mapmaking expedition to the undefined and much-disputed Brazil-Bolivia border, Fawcett quickly assembles his team and basically tells Nina, “See you in a couple of years.”

A bespectacled, thickly bearded, almost unrecognizable Robert Pattinson gives a strong performance as Fawcett’s loyal and brave partner-in-exploration Henry Costin. Fawcett, Costin and a small band of hearty adventurers sport crisp outfits, jaunty hats and unbridled enthusiasm when they first set out on the Amazon — but it doesn’t take long before they’re exhausted, drenched in sweat, fighting off all manner of insects and sea creatures, and on the brink of starvation.

Not to mention the natives who greet them with hails of arrows so thick they nearly darken the sky.

Yet it all seems worth it when Fawcett discovers a few artifacts and carvings pointing to the existence of a lost city populated by an advanced civilization that created pottery, farmed the land using relatively sophisticated methods and built architecturally impressive structures.

One of the most entertaining scenes in “The Lost City of Z” transpires back in London, where Fawcett makes his case in a public forum and is greeted with much derision from British gents who are threatened by the mere suggestion there might have been a civilization even older and at least as advanced as their own. Why, it’s blasphemy!

With Christopher Spelman’s rousing score and cinematographer Darius Khondji’s spectacular work setting the tone, Fawcett returns to the Amazon again — and again. He doesn’t consider the natives to be ignorant savages; in fact, he greets them with deference and great respect, and asks for their help in guiding him to the ruins of the lost city.

“The Lost City of Z” is filled with remarkable, unforgettable scenes, as when Fawcett and his party stumble upon a makeshift but elaborate opera house run by a rubber plant baron in the middle of the jungle.

When Fawcett isn’t exploring the Amazon, he’s fighting with his mates at the Battle of the Somme in World War I (a brutally effective but perhaps not altogether side journey for the film), or attempting to reconnect with this family. (It seems as if every time Fawcett leaves, Nina is pregnant, and by the time he returns, the child is walking and talking and doesn’t recognize Pops.)

Sienna Miller has played the understanding wife in film after film and she always adds dimension to the character. As much as Nina supports her husband, she has an adventurous side herself — she even proposes going along on one of the expeditions — and she grows weary of Fawcett saying, “We all have to make sacrifices,” just before he rides off for another adventure with his colleagues while she’s left at home to raise their children on their own.

Hunnam expertly conveys Fawcett’s bravery, spirit and sometimes reckless nature. At times we sense even he knows he might never find absolute proof of the City of Z — but he’ll die trying if he must.

★★★1⁄2

Bleecker Street presents a film written and directed by James Gray. Rated PG-13 (for violence, disturbing images, brief strong language and some nudity). Running time: 140 minutes. Opens Friday at local theaters.