ONE of the great unsolved exploration mysteries in recorded history gets the big-screen treatment here.

It's the tale of of English explorer Colonel Percival Fawcett (Charlie Hunnam) who became obsessed with finding a long lost city of gold he called Z (pronounced “Zed”) said to be hidden within the depths of the Amazon jungle.

Eventually he led an expedition in 1925 into uncharted Amazonian territory before disappearing without a trace. But this isn’t a film about the end goal as such – some revelatory hidden stash of treasure just waiting to be found by a plucky explorer with pound signs in his eyes – but rather our protagonist’s obsession with reaching something forever exceeding his grasp.

Director James Gray (The Immigrant, Two Lovers) seizes the opportunity to explore the idea of unwavering obsession, stalwart determination and idealistic ambition as a means to answer an ever-present inner calling rather than evidence or the word of other explorers, which was tenuous at best and practically non-existent at worst.

He does this even if that means being openly mocked by his peers with scoffs and shouts of “fool!” back in the stuffy halls of old England at his self-imposed, perceivably foolhardy mission. He has merely a handful of fellow travellers – chiefly Corporal Henry Costin (Robert Pattinson, compellingly quirky and almost unrecognisable under a grizzly beard) – crazy enough to go along with him.

This ever-present need to get out there and discover puts a strain on his life back home, including his marriage to wife Nina, played wonderfully by Sienna Miller, who continues her run of bringing depth and pathos to potentially one-note supporting wife and lover roles.

Their relationship becomes increasingly strained by time apart and promises that, really, this will be the last time he goes; absence may make the heart grow fonder but it doesn’t stop the separation from hurting. At the same time he misses his children growing up, knowing their father more by reputation or motherly reassurance than consistent paternal affection. The fascination isn’t over whether or not it’s worth it but in Fawcett’s inherent need to find out.

Hunnam throws off his macho hunk persona seen in the likes of TV’s Sons Of Anarchy and Guillermo del Toro’s monster blockbuster Pacific Rim to give a more nuanced, composed performance that conveys, often with mere glances, the angst and wide-eyed wanderlust of the central figure. He’s the beating heart of this powerfully measured, handsomely mounted film that’s awash with a grand sense of scope and scale and is the better for taking its time.

The deliberate pace allows for the palpable atmosphere to wrap around you like a cloak and sense of exotic place to take hold to make sure you feel transported back in time and away to somewhere at once tantalisingly tangible and alluringly mystical; Werner Herzog’s Aguirre, The Wrath Of God and Francis Ford Coppola’s Apocalypse Now are just a couple of its influential touchstones, though Gray’s enigmatic adventure carves out a place all of its own.

It makes for a richly rewarding piece of cinema, more interested in making you think than chucking action at you every five minutes, unafraid to hold its themes of relentless obsession and steadfast ambition aloft at the forefront of the grand, sumptuous voyage. This is a carefully crafted love letter to old-fashioned adventure cinema that seemed to have sailed away long ago.