SAN FRANCISCO — If it weren't for Google Inc. trying to cover it up, the old sea-worn barge stacked four stories high with customized shipping containers may not have become an object of global fascination.

SAN FRANCISCO — If it weren't for Google Inc. trying to cover it up, the old sea-worn barge stacked four stories high with customized shipping containers may not have become an object of global fascination.

But Google being Google with all its out-there projects — many ripped from the pages of sci-fi bestsellers — the secrecy behind the barge has taken on a life of its own. Google isn't saying anything, and having guards shoo away prying eyes has only added to the mystery.

Since the barge was discovered 10 days ago, my imagination has raced through mind-blowing possibilities. What could be next for a company funding projects to end death, build robotic cars and take the Internet to outer space? A teleportation device? A time-travel machine? The world's largest Easy Bake Oven to make 8-foot-high cupcakes?

Or perhaps it's just an epic marketing prank to get us all talking about Google.

"This is like catnip for conspiracy theorists and nerds," said Paul Saffo, a consulting professor of engineering at Stanford University and a Silicon Valley technology forecaster.

The barge became my Area 51, the secretive military base in Nevada that every amateur sleuth has tried to uncover. Piercing Google's defensive shields was going to be tough, but I was undeterred. I picked up my notebook and camera and set off from my home in Oakland to find the truth.

To get there, I drive west across the gleaming new eastern span of the San Francisco-Oakland Bay Bridge, which recently opened. At about the halfway point to San Francisco, just before the thoroughfare enters a tunnel, I turn off the exit for Yerba Buena Island onto a road that swirls around the island before taking me north to my destination.

That road connects to Treasure Island, a man-made no-man's-land trapped in limbo between its past as a U.S. naval station and its destiny as a proposed business and residential development with million-dollar views of the city.

The entrance to the pier is secured by two wooden guard stations. A guard politely declines my request to venture out for a closer look. The structure on the barge remains partially wrapped by a white covering. Two workers are installing a chain-link gate topped with barbed wire to keep the curious out.

I turn around and face Hangar 3, which is about a football field away, separated from the pier by the street and a large parking lot that has also served as a helicopter landing pad. This 67,000-square-foot warehouse is where the structure was built, though there is little activity on this day.

I approach the hangar, where signs warn "Danger: Do not enter" and "Please prepare to surrender your smartphone, camera phone, camera, and or any other audio/visual devices." The hangar door opens and a flatbed truck slips inside before the door quickly shuts.

I then walk around the building to Hangar 2, home of a company called Island Creative Management, which produces large-scale tech events and conventions. A friendly employee tells me the owners had signed a nondisclosure agreement to not discuss their neighbor's project.

I go back to Hangar 3 and circle it again before crossing the street to Yerba Buena Builders, a construction company, where I meet Keith Miller.

Miller smiles as I approach, clearly amused by the buzz of media interest since CNet reporter Daniel Terdiman broke the story. His story speculated that it might be a floating data center, based on patents Google had received for using seawater to cool such a thing.

But if the project were a secret, it was hidden in plain sight, Miller says.

For months, TV news crews parked along the street as they did stories about the new Bay Bridge construction. Miller was tickled that they never seemed to point the cameras in the other direction and wonder about the activity taking place in and around Hangar 3.

"I thought there must be a media blackout or something," he says.

Late last year, a 5-foot-high fence was erected around the Hangar 3 parking lot, and hundreds of laborers, welders and plumbers descended on the site, working at least two shifts a day. When Miller chatted with them, they said they had no idea what they were making or who they were doing the work for, though some had apparently guessed it was Google.

Each day, a bunch of large metal shipping containers would be hauled into the site, where they were taken apart, modified, reassembled and eventually stacked on top of one another. Some had the sides cut out and large picture windows installed.

Eventually, the containers were stacked into a single rectangular structure — four shipping containers long, four containers wide, four containers high — and transported to the end of the pier and placed on the barge. And then, it seemed, everything came to a halt.

The company that held the hangar lease when the work started was G & K Media, a Spokane, Wash.-area firm that produces special events for large corporations. According to the lease, the purpose was "Fabrication of a special event structure and art exhibit only and for no other purpose."

The lease was signed by Kris Hemenway-Sheets, whose LinkedIn profile describes her as a "line producer" for the media production company. Reached by phone Friday, Hemenway-Sheets says she signed a nondisclosure agreement and can't talk about the project.

"I have to remain silent on this for now," she says. "It's going be fun. I'll promise you that."