Rare behind-the-scenes photos show Muhammad Ali training for one of his most historic fights

In August 1974, photographer Peter Angelo Simon ventured to Deer Lake, Pennsylvania, to document Muhammad Ali at his remote training camp, "Fighter's Heaven." At the time, Ali was prepping for what would be one of his most historic fights: the world heavyweight championship against George Foreman. Ali had dubbed the fight "The Rumble in the Jungle."

Simon wasn't sure what to expect. "I had never been to a boxer's training camp," he wrote in the intro to his upcoming book "Muhammad Ali: Fighter's Heaven 1974." It's an especially timely piece given Ali's passing June 3.

"While a global audience was fixated on his fate, I was able to record aspects of Ali virtually unknown," Simon said in a press release for the book. Ahead, see some of the intimate moments Simon captured of one of the world's most famous boxers.