Alcatraz Island, referred to colloquially as ""the Rock,"" was converted from a military stockade to a federal maximum security prison in the 1930's to house some of America's most dangerous criminals. Alcatraz was supposedly inescapable, but in 1962 three inmates would stage a daring escape attempt that continues to impress experts to this day. Tune in when The UnXplained returns this Saturday, July 11th at 9/8c to learn more about Alcatraz and some of history's greatest escapes. | HISTORY