Call me perverse, but for me this one was definitely a no-brainer. Big sexy photos you can see any time. But how often do you get the chance to take part in a mass test of London’s famously wobbly Millennium Bridge? The one which caused such all-round hilarity when it was forced to close in June 2000 just three days after opening in a fanfare of tub-thumping, jingoistic publicity?

Such high-concept pedestrian bridges are now as much of a status symbol for world cities as funny-shaped art museums or opera houses. They are part of the new, humane, people-first image that cities like to project. So if they go wrong, unpleasant body products tend to hit the fan. Lord Foster, architect, and his engineers, Arup, had staked their reputations on designing a bridge that would be almost impossibly slender. A suspension bridge stretched so taut, it did not need towers to hold it up, merely a pair of forked sticks in the river. They called it “the Blade of Light”. To me, it always looked like a snake, draped over those sticks. And, as all the world knows, they goofed. The Blade turned out to be rather too flexible. The snake writhed. At a charity walk across the newly-opened bridge, people found themselves unaccountably staggering from side to side as if on the deck of a ship in rolling seas. The bridge was promptly closed. Back to the drawing board, as they used to say.

After that searing embarrassment came a period of intense research. “We wrote the equivalent of three or four PhDs in a few weeks,” one Arup engineer told me. They sorted out a fix - an assortment of spring-loaded dampers and struts, most placed unobtrusively below the bridge deck. But their computers had let them down before. So once the £5m of repairs had been made, there was no alternative: they had to get a lot of people to walk over it, all at once, and watch very carefully. This, then, was finally the crucial moment. Had they got it wrong again? I decided Kate Moss could wait. Off to the bridge I went.