From aish.com
1942 in Perigueux, France, a few men hurried into a rundown wooden barrack. Each opened the door carefully looking around to make sure they weren’t being followed. They then went into a hidden backroom. This room served as the makeshift Shul for those brave enough to venture out. The "shul" barely scraped together a minyan of men to pray.
They davened Maariv quickly, their hearts rapidly beating with the knowledge that at any moment the Nazis could storm in and arrest everyone. One man lit the menorah as the others ran to grab their coats and get home as fast as possible.
Suddenly, a man in the back of the room stood up and in a deep, warm voice started to sing “Maoz Tzur.” The men were frightened and aghast. Someone might hear; it was too dangerous! Soon another man joined in singing, then another and another, until everyone was tearfully and courageously singing with joy. For the moment, gone were the fears of the Nazis. For a few moments, Chanukah was there in all its glory, as in days of Judah the Maccabbe, a few brave men stood proud, their faith prevailing over the evil surrounding them.