There is something special about the Pak Ou Caves, a delicate combination of age, remoteness and simplicity that lends the shrines an earthy authenticity. It’s something to do with riding a pirogue two hours upstream from Luang Prabang, then stepping off the Mekong straight into a towering cliff face. Something about inching your way 50 metres inside a darkened chamber with a dirt floor and walls of living rock, to find yourself, as your eyes grow accustomed to the dim light, staring at hundreds of graceful gold lacquered Buddhas, ranging in size from no larger than your thumb to as tall as a human.

They stand in higgledy-piggledy rows on shelves of stone, or in tight huddles in little roughhewn alcoves. Some wear carved robes finished in crimson, and enigmatic smiles on their faces. Others have elongated, curving arms reaching almost to their feet. Almost all of them carry the slender elegance of the Luang Prabang Buddha and the dark burnish of antiquity. Daring as far back as the 17th century, some look like they would crumble at a touch.

The problem confronting Benita Johnson is how to preserve this unique site without losing its character. One month every year since 1992, the Canadian-born conservator has led a team from Australia’s University of Canberra charged with restoring and protecting the two caves. The project has been funded by Australia’s overseas aid agency, AusAID.

The caves once fell under royal patronage, and monks from a nearby village were responsible for their upkeep. But the site has suffered decades of neglect, and among the problems the Australian team had to confront on its first visit were bars, borers, termites and wasps. Another unwelcome surprise was a box of live ammunition, presumably left there during the war. "I don’t know how that was disposed of," says Ms Johnson. "We told the authorities about it and they got rid of it."

But the most pressing issue now facing the four conservators is how to manage the increasing numbers of tourists visiting the caves. One of the big problems is getting people not to touch the fragile carvings.

"I would like to see visitors restricted to small groups, and kept under constant supervision by guides while they are in here," says Ms Johnson. Security at the caves has been beefed up, with four guards now on site. Additional measures include hand rails to keep the Buddhas out of reach, stabilising the floor surfaces, and signs explaining the significance of the site.

Ironically, visitors from Buddhist Thailand, by showing respect for the images, may be inadvertently endangering them. "There’s one practice I haven’t made up my mind about yet," says Ms Johnson. "For the last few years, Thai visitors have been placing new sculptures in the Lower Cave. Also, in the last year, small squares of gold leaf have appeared on three of the images, which is a way of showing respect in Northern Thailand and Burma.

"This means that they’re revering the sculptures, and that’s great. But that isn’t done in Laos, so in a sense they’re interfering with the artistic intent of the sculptures, and once the gold leaf has been attached to the sculpture, it can’t be removed."

Another priority is to protect the floor of the caves from interference, as they may contain a rich archaeological record that awaits excavation. Little archaeological research has been done at the caves, but some resin figures indicate that the site may have been used for spirit worship prior to the 16th century, and ceramic shards have been discovered which may be prehistoric.

Traditionally, Lao monarchs visited the caves once a year at Pimai, or Lao New Year, and commissioned statues to be placed inside them. Devout visitors could also place carvings in the shrines, and the site is still a popular spot for locals to visit at Pimai and wash their household Buddha images. Altogether, there are about 4,000 Buddhas in the two caves. Some of them are made of resin, or soapstone, or sandstone, or horn, but mostly they are of carved wood finished with lacquer and gold leaf.

One of the biggest tasks has been to catalogue the Buddhas. Although some repair work has been done on broken images, there is little that can be done to restore many of the wood carvings that have been attacked by insects or brown rot. "We can lift the figures off the ground, but that won’t stop the humidity or attack by flying insects," says Ms Johnson.

But to remove the Buddhas to a museum would be to take them out of context and destroy their unique milieu. Instead, the team has opted to try to stabilise the environment inside the caves as far as possible.

I ask Ms Johnson if anything will be done about the lighting in the Upper Cave, which has no artificial lighting at all and is very dark in the interior.

"Excuse me while I cringe," she says. "First of all it would require a generator. Having lights would raise the temperature for short bursts of time, which creates an unstable environment and raises humidity. And it would destroy the atmosphere inside the cave. You would lose the sense of wonder. I would prefer just to hire flashlights to tourists, or to use candles."