Cambodia's lost temple, reclaimed from the jungle after 800 years

The haunting monastic complex is so entwined in jungle vines and mystery that it could be the set of an Indiana Jones film. But it is not. It is one of the great historic treasures of south-east Asia, and is slowly awakening after eight centuries of isolated slumber.

The dramatic towers, bas-reliefs and dark chambers of Cambodia's Banteay Chhmar make it a far more atmospheric place than its famous twin at Angkor Wat. What drove Jayavarman VII, regarded as the greatest king of the Angkorian Empire, to erect this vast Buddhist temple about 105 miles (170km) from his capital in Angkor, and in one of the most desolate and driest places in Cambodia, remains one of its many unsolved riddles.

Called the "second Angkor Wat", Banteay Chhmar approaches it in size, is more frozen in time than the manicured and made-over superstar, and has so far been spared the blights of mass tourism of recent years at Angkor. In 2011, an average of 7,000 visitors a day went to Angkor, making it one of Asia's top tourist draws. Banteay Chhmar, meanwhile, saw an average of two a day, with no tour buses and bullhorn-wielding guides to disturb the temple's tranquillity or traditional life in the surrounding village.

Abandoned for centuries, then cut off from the world by civil war and the murderous Khmer Rouge, Banteay Chhmar didn't welcome visitors until 2007, when the last landmines were cleared and the looting that plagued the defenceless temple in the 1990s was largely halted. A year later, the California-based Global Heritage Fund began work at the site under the overall control of the country's Ministry of Culture, and now spends about $200,000 a year on the project.

John Sanday, a veteran British conservation architect, assembled a team of 60 experts and workers, some of whom were with him on an earlier restoration of the Preah Khan temple at Angkor. Others were recruited from the surrounding community, and, although they are barely literate, Sanday says they're among the best he's worked with in Asia. Challenging them are hundreds of thousands of stone blocks from collapsed shrines and galleries scattered within the 4.6-square-mile archaeological site. Towers teeter, massive tree roots burrow into walls, vegetation chokes a wide moat girding the temple.

Three-quarters of the bas reliefs – rarely found at other Angkorian temples – have fallen or been looted, the most notable being eight panels depicting Avalokiteshvara, an enlightened being embodying Buddhist compassion. Thieves sheared off four panels with jackhammers, smuggling them into nearby Thailand where two are widely believed to be decorating the garden of a Thai politician. A pair has been recovered and the others are still at the temple, although only two still stand.

"We've been struggling away with this gallery for nearly two years now," says Sanday, at another bas-relief, one depicting a figure believed to be Jayavarman VII leading his troops into battle. In vivid detail, the ancient sandstone wall springs to life with charging war elephants, soldiers plunging spears into their enemies, and crocodiles gobbling up the dead. Nature and time have proved the culprits: the vaulting protecting the 98ft-long relief collapsed, exposing the wall to monsoon torrents, which seeped downwards to wash away the masonry and loosen the foundations. Pressure from the weight above toppled sections of the wall or forced it to lean.

Nearby, two young Cambodian computer whizzes are pioneering a shortcut to the reassembly process through three-dimensional imaging. The work-in-progress is one of the temple's 34 towers recently damaged in a severe storm. Some 700 stone blocks from the tower have been removed or collected from where they fell, and each one will be videographed from every angle. Since, like a human fingerprint, no two stones are exactly the same, still-to-be-finalised software should be able to fit all the blocks into their original alignment after they are repaired. "We hope that with one push of the button all the stones will jump into place to solve what we are calling 'John's puzzle'," says Sanday.

When an original block is missing, or is beyond repair, another original stone from the site can be used or, as a last resort, a new stone will be inserted. "My philosophy is to preserve and present the monuments as I found them for future generations without falsifying their history. So often people tend to guess what was there," says Sanday.