While most people think of San Francisco as a haven for peace-loving hippies, this city by the Bay is actually one of the biggest military defense installations in America. We'll take you beneath its picturesque hills and uncover the biggest ammunitions depot on the West Coast before plunging into a deadly arsenal that once stored nuclear missiles with more than six times the destructive power of the atom bomb dropped on Hiroshima. From the secret Civil War fortification buried beneath Alcatraz to the human trafficking tunnels winding below Chinatown, San Francisco's underground is evidence of its sordid past.