Secret Tunnels Under San Francisco?

<p>San Francisco is 49 square miles, but contains more than 1,000 miles of sewer mains, running under every block. Take a trip with Bay Curious reporter Carly Severn into the depths of the city, and discover an otherworldly cave that has reached legendary status with some urban explorers.</p><p>VIDEO: Take A Trip Into San Francisco's Sewer System</p><p>Web story: Tunnels Under San Francisco? Inside the Dark, Dangerous World of the Sewers</p><p><br></p><p>Reported by Carly Severn. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Suzie Racho and Rob Speight. Additional support from Ju...