… some of the Jewish people survived WWII by hiding in the sewer system?
As the Nazis were killing the last of the Jews left in the Lvov ghetto, a man named Ignacy Chiger dug a tunnel into the sewers and saved his family and fifteen others.
However, sewer workers discovered them. One man was Leopold Socha. He and the other workers, for money, brought them food, water and news. When their money ran out, Leopold continued to help them anyway.
Of the original 21 persons, 10 of them survived the war. After more than one year, Socha led them out when the Nazis left the area.
It is estimated that about 200,000 Jews survived in hiding. It would not have been possible except for those who helped them. Rescuers were routinely executed for their compassion.
-Imperial War Museum Holocaust Exhibition