Yesterday was a fine evening for London's monthly Critical Mass ride. There's always a great atmosphere as everyone gathers by the National Theatre at the South Bank.
Cyclists are a very diverse bunch: from crisp business suits on Bromptons, to dreadlocked and tattooed alternative types who display their piercings in curious and intimate places, such as just under Waterloo Bridge.
There's no starting-gun or fixed time. However, a kind of consensual crescendo of bells, whistles, irritatingly loud bike-trailer sound systems, and everyone on their mobile saying 'It looks like we're setting off, I'd better go', catalyses the grand départ shortly after 7pm.
Where it goes from here depends on the whim of the crowd - it could go literally anywhere in London - but even if you don't want to or can't join the ride, the start is a remarkable and thrilling sight.
There are lots of rather puzzled tourists watching too. If you listen to them carefully you can learn how to say 'What's this?', 'I don't know', and 'Where's the bar?', in a range of European and Asian languages. Which luckily is all you'll need to know when you travel there.
Through summer, this also happens to be the venue for free nightly outdoor entertainment. You can sit on the astroturf outside the National Theatre and enjoy world music bands or circus-style entertainment with a beer or glass of wine from the bar.
On Critical Mass nights, though, the acts have tough competition from the cyclists. Watching them is an entertainment in itself.