Brick by brick, plank by plank, workers at the former Nazi German death camp Auschwitz-Birkenau carefully clean its barracks to preserve the Holocaust symbol for future generations.
"This is the largest preservation project in the history of the museum at Auschwitz-Birkenau. It's unprecedented," museum spokesman Pawel Sawicki told AFP.
Along with the ruins of the gas chambers and crematoria, the barracks bear witness to Nazi Germany's killing of around 1.1 million people, mostly Jews, at this camp, which it built in 1940 in the southern city of Oswiecim after occupying Poland.
"Preserving a barrack requires a completely different approach than one used to preserve a church for example. There, the goal is to return the building to its original state, so its most beautiful state," says site manager Ewa Cyrulik.
"Here, the goal is to leave everything unchanged. The biggest compliment for us is when someone says they can't really see a difference afterwards," she tells AFP.
The task is all the harder because these types of poorly constructed barracks have never been preserved before, according to the Auschwitz team.
"My colleagues in the building industry laughed when I told them what I was doing. They said it'd be easier to just tear down the wall and rebuild it brick by brick than to restore it the way we're doing," says Szymon Jancia, a construction expert at the site.
"We're aware that people come here specifically to see authentic objects and buildings," Cyrulik adds for her part.
Protected from the weather by tents 12 meters (39 feet) high, the two barracks under restoration number among the camp's oldest.
Work on the barracks began in September 2015 and will continue for another couple of years, while the entire project will take more than a decade and cost millions of dollars.
- Fragile buildings -
Auschwitz-Birkenau is really two camps, located three kilometers (two miles) apart.
While Auschwitz has been subject to preservation work in the past, none of the brick barracks at Birkenau have been seriously restored before.
Only simple maintenance work was carried out to respond to critical repairs.
Birkenau's buildings are much more fragile than those at Auschwitz, which were built long before Nazi Germany took them over and originally served as military barracks.
Birkenau's buildings on the other hand were meant specifically for the camp and were built in a slapdash manner, using less robust materials.
Their walls are thin, barely the thickness of a brick, and have buckled in places because the roof is too heavy. The wooden frame is rotting. The foundations have been eroded by groundwater.
"It's a miracle they're still standing," says Jancia.
In total, 45 brick buildings at Birkenau will undergo restoration work.
The team will preserve whatever parts are in good condition, and replace those that are in a poor state or threaten the integrity of the entire building.
"Whatever we replace has to be visible to the eye, so as not to be confused with the original," Cyrulik says while pointing to layers of paint in a slightly different color.
- Model wall -
Kneeling in a cramped hole, workers carefully remove earth to get at the foundations that have been weakened by groundwater.
They work by hand, without recourse to machines, as is the case elsewhere on-site.
Inside a nearby tent, they have built a six-meter-long model wall that is propped up by metal bars.
"It's a wall we built using the same materials and featuring the same flaws as those in the actual barracks," Jancia says.
"It lets us test preservation methods. The walls are held up by the very same car jacks used for changing a tire."
The entire project has so far cost $2.9 million in funding secured by the Auschwitz-Birkenau Foundation.
Created in 2009, it manages the funds meant to preserve the site of the former Nazi German camp.
To date, donors have contributed 101 million euros, including 60 million from Germany, as well as big donations from the United States, Poland, France and Austria.