Google has something big and mysterious in a box, on the sea. And it's not saying what's inside.
According to various local reports, a barge linked to Google is currently moored to San Francisco's Treasure Island. It's at least four shipping-containers high, and no one seems to know what's inside.
CNet and San Francisco CBS TV station KPIX have both reported that Google is either responsible for the barge, or involved in it being there.
So what's inside? And why can't it come ashore?
So far there are two possible explanations floating around (no pun intended). CNet speculated that it might be some kind of data centre. But according to CBS, it's actually "a floating marketing center" for Google Glass, its gradually evolving wearable computer.
The idea is that maybe Google has built a giant Apple store-like centre on the barge, and will move it around to promote the device - or just use it to get around San Francisco's property prices by mooring it close to Fort Mason.
The problem, CBS explains, is that it doesn't have a permit for the structure and so work has halted despite it spending "millions" on getting the idea ready for a US rollout of the product. The site quotes San Francisco Bay Conservation and Development Commission officials who admited "hypothetical operations" discussions with the company, while claiming nothing is decided.
So for now we don't know what's inside - and we won't until Google decides to tell us, and the City...