Dug straight into the side of a massive mountain, the horizontal mine was impregnable to aerial bombardment—even if the bombers could locate it in the vast Sandling mountain range. The salt in the walls absorbed excess moisture, leaving the humidity constant at 65 percent. The temperature varied only between 40 (in the summer, when the mine was coolest) and 47 degrees Fahrenheit (in the winter). The environment helped to preserve the paintings and prints,
