A perfectly masterminded plot leads to one of the most brazen prison breaks in American history. With only a handful of clues left behind, the search for the infamous Alcatraz escapees continues to this day. But is it really possible they survived -- and if so, where did they go?

With 500-year-old secrets hidden in skeletons and stone, Machu Picchu is one of the most puzzling archaeological sites on earth. It's among the ancient world's most enduring riddles: Who built this astonishing complex, and why?