In April 1945, crates labeled "Marble – Do Not Drop" were carried deep into a salt mine in the Austrian Alps. They weren't marble. They were 500-kilogram bombs. The Nazi gauleiter of the region, August Eigruber, wanted to blow the mine before the Allies could reach it. Inside were thousands of stolen masterpieces, including Michelangelo's Bruges Madonna, the Ghent Altarpiece, and Vermeer's The Art of Painting. Local miners quietly pulled the bombs out and sealed the entrances before he could follow through. A few weeks later, two American soldiers squeezed through a small opening into the mine. One of them, Lincoln Kirstein, would later co-found the New York City Ballet. They were Monuments Men. The Monuments, Fine Arts, and Archives program was about 345 men and women from 14 countries. Museum directors, curators, architects, art historians, librarians. Most were too old for normal combat roles, and many had never fired a weapon. They went into the war zone anyway, often with no vehicle, no staff, and barely any authority, armed mostly with lists of churches and buildings the Allies were supposed to avoid bombing. Then they started finding what the Nazis had stolen. It was everywhere. Castles, salt mines, monasteries, private homes. Neuschwanstein, the fairy tale castle in Bavaria, was packed with art looted from French Jewish families. Much of it was found because of Rose Valland, a quiet French museum employee in Paris who spent four years secretly writing down everything the Nazis shipped out of her building, where it came from, and where it was going. The Germans had no idea she could understand them. One of the most remarkable stories belongs to Harry Ettlinger. He was a Jewish teenager who fled Karlsruhe, Germany in 1938. As a boy he'd never been allowed into the city museum to see its famous Rembrandt self-portrait, because Jews were banned. Seven years later he came back wearing a US Army uniform, working in a salt mine near Heilbronn, and found that exact Rembrandt sitting in the dark. He finally saw it for the first time in his life. Two Monuments Men were killed in action. Walter Huchthausen, an American architect, was shot while trying to recover an altarpiece near the front. By the end, they had helped recover and return an estimated five million artworks and cultural objects. They kept working for six years after the war, returning pieces to the countries and families they were taken from. Almost all of them went home and went back to quiet museum and university jobs. Most of America never knew their names until 2015, when they were awarded the Congressional Gold Medal.