For centuries, the Lithuanian city of Vilna was one of the most important Jewish centers in the world, earning the title “Jerusalem of the North” until World War II, when the Nazis murdered about 95% of its Jewish population and reduced its synagogues and cultural institutions to ruins. The Soviets finished the job, paving over the remnants of Vilna’s famous Great Synagogue so thoroughly that few today know it ever existed. Now, an international team of archaeologists is trying to rediscover this forgotten world, excavating the remains of its Great Synagogue and searching for proof of one of Vilna’s greatest secrets: a lost escape tunnel dug by Jewish prisoners inside a horrific Nazi execution site.