The Amber Room, a priceless chamber looted by the Nazis during World War II, has been missing for some 70 years, but a German retiree claims to be honing in on its location, reports Reuters.

Called the eighth wonder of the world, the Amber Room, covered in amber panels, gold, and gems, was constructed between 1701 and 1709 for the palace of King Frederick I of Prussia. The room was later given as a gift to Peter the Great, czar of Russia, and is thought to be worth anywhere from $140 to as much as $500 million.

Nazis seized the room while invading St. Petersburg in January 1941, and transported it to Königsberg, Germany. From there, the trail runs cold, despite the best efforts of generations of hopeful treasure-hunters. Though many suspect the Amber Room became a casualty of war, Karl-Heinz Kleine, a 68-year-old pensioner, may have a new lead.

Kleine’s theory is that a Nazi official named Erich Koch smuggled the room to his hometown of Wuppertal, where it could still be secreted away in a hidden bunker or underground tunnel. Koch was convicted of war crimes, and was known to have shipped looted art away from Königsberg during the final months of the war.

A company had lent Kleine a drill to conduct his search, but they have since asked for it back.  “The search is very costly. We need helpers, special equipment and money,” Kleine told Reuters. “I am optimistic. I just need the tools, then it could go quickly.”

The Amber Room was just one of many artistic treasures stolen during the war, and many Nazi-looted objects are only now being returned to the families of their original owners (see Oxford’s Ashmolean Museum Returns Nazi Loot and New Trove of Nazi Looted Artworks Found in German Museum).