Robert Edsel, author of “The Monuments Men,” came to town the other day with a heavy album bound in green Moroccan leather. “Gemäldegalerie Linz XIII” was embossed on the spine. Inside were black-and-white photographs of mostly obscure 19th-century German paintings.

The album was one of the long-missing volumes cataloging the never-built Führermuseum in Linz, Austria, which Hitler envisioned someday rivaling Dresden and Munich. Starting in 1939, Nazi henchmen and art dealers bought and stole thousands of paintings, sculptures, tapestries and other objects from private collections across Europe, then stockpiled them. Hitler helped draw up architectural plans, which megomaniacally grew to include a theater and an opera house, a hotel, a library and parade grounds. Photographs show him, pencil in hand, pondering plans and gazing raptly on the model for the site.

“And so they are ever returning to us, the dead,” the German novelist W. G. Sebald wrote in “The Emigrants.” “At times they come back from the ice more than seven decades later and are found at the edge of the moraine, a few polished bones and a pair of hobnailed boots.” He was recalling a long-forgotten Alpine climber, whose remains a glacier in Switzerland suddenly released, 72 years after the man had gone missing....