My first thought when I read this task was the Marriott on 4th in downtown San Francisco. I've been all up and down it, as have many people. In previous spelunking exhibitions, I'd been to the bar on the top floor, across multiple floors in between, and once down the stairs and out through the employee exit. For SF0, however, I wanted to plumb the depths and find the long-foretold secret passage. I'd heard about it in the past from an ambassador in the city, but I'd never found it. Today, I decided to find it.