Running breathlessly through the centre of San Francisco as the sky blazed with the beginnings of a beautiful sunset, we burst into the doors of the posh hotel with the famous rooftop bar, startling the wealthy clientele. But our haste was in vain. When we found him, the concierge told us that the bar wouldn’t open until eight, which would be long after dark on this late-December evening.

Andy and I reluctantly abandoned his surprise idea of sipping cocktails while watching the sun go down over the city, and wandered around in search of some other special way to end the day.

We took a turn around Union Square, enjoying the spectacle of the Macy’s Christmas tree and teenagers teetering on a temporary ice-rink. In the lobby of The Westin St Francis, the world’s biggest sugar castle revolved slowly inside a circle of entranced children, complete with a sugar steam-train. And, as we turned towards the bar, Andy bumped into a friend from his Silicon Valley days. He was carrying what appeared to be several squashed surfboard cases.

“We’re having a jellyfish bloom here tonight,” he said cryptically, gesturing at his luggage. “Come and join us.”

As we sipped on festive hot cocktails with whisky and pumpkin cream in the Westin’s ruby and amber-lit bar, Andy explained that his friend, Rob Lord, had started the Burning Man performance art piece Billion Jelly Bloom. We had just been invited to participate in a flash bloom – a flash mob performance in the streets of downtown San Francisco of these fantastic 15-foot tall kinetic jellyfish.

Later that evening, when we knocked on the door of Rob’s suite, this is what we found…