"G.I. Joe" and "American Sniper" actress Sienna Miller has revealed she is set to join filmmaker James Gray's Amazonian mystery feature "The Lost City Of Z". Benedict Cumberbatch plays Colonel Percival Harrison Fawcett, a former decorated British soldier turned early 20th century explorer. Fawcett and his son disappeared in 1925 during an expedition to find the ancient and lost 'City of Z' in the uncharted jungles of the Amazon. Over the next seventy years, scores of explorers tried and failed to retrace Fawcett's path, including a 1996 expedition of Brazilian adventurers.