These men are singing Amazing Grace in the Roman Colosseum. This is the location where thousands of Christians were put to death for their faith in the Lord. In Fox's Book of Martyrs it states that most of the Christians killed here were fed to lions or stoned. In the video you will see that it is lit with huge spotlights. However, during the times of Christian persecution, when it got dark, the emperor would choose many of the Christians to be nailed to crosses around the stadium and rubbed down with tar and lit on fire to light the arena.
I don't know if the men who are singing this are Christians. But as a Christian, I can't watch this video and think about what happened here and what thousands of men and women were willing to do for the Lord and not feel ashamed.