Robert Marshall's "In the Sewers of Lvov" was very hard to find, but I managed and was rewarded deeply. This is the story of a group of Jewish people who survived the Holocaust by hiding and living their lives in the sewers of their city, Lvov, for over a year. With the help of a municipal sewage worker, they survived and were able to return to daylight after the liberation by the Russians. 

This book is truly unforgettable. There's also a movie though it's not very good and falsified a few things.