There is perhaps no lost-treasure mystery more seductive than that of the priceless Amber Room of Peter the Great, which disappeared in the chaotic closing hours of World War II. Now Bartlomiej Plebanczyk, an unassuming historian and museum director in northeastern Poland, believes he has found it.

Elderly villagers told Mr. Plebanczyk that they had seen a German convoy unloading big crates into a secret chamber in a stark, moss-covered Nazi bunker near the Russian border in early 1945. So the Mamerki Museum, whichhe leads, recently completed a ground-penetrating radar scan of the derelict bunker that he said confirmed the existence of a hidden chamber.

“This is the perfect place to hide something if you have to move it quickly out of eastern Prussia,” Mr. Plebanczyk said.

Poles are used to hearing extravagant tales of lost war loot, and also to hearing the tales debunked. Last year, two men claimed to have found a buried train containing Nazi gold, but an investigation found no such thing. Despite that, war-treasure hunting is such a popular pastime in Poland that enthusiasts have their own web forum.