Watch Secrets of the Great Wall (1970) : Full Movie Online Free The Great Wall of China stretches for thousands of miles, an iconic monument that can be seen even from outer space. Yet, despite being so visible, it's steeped in secrets, which are finally revealed in this extraordinary documentary produced by the Discovery Channel (with the help of NASA and various Chinese organizations). Learn about the history of the wall's construction, including the impetus for building it and lives lost in its creation.