Spontaneous Gatherings

You've heard of them. Suddenly your supermarket becomes a madhouse of teenagers racing in shopping carts. Your bank gets invaded by hordes of zombies... your local park is overtaken by medieval jousting knights...

When I was working at the bookstore, suddenly a huge group of teenagers files in, looking nervous and self-important. I was hoping for a Spontaneous Gathering, but no, they were just meeting up somewhere before heading to a concert. And I was sad. :(

Here's a fantastic example of spontaneous gatherings. Watch this video if it's the only thing you do today, because it's fantastic.

And hey, get together a group of your friends and go out and do something creative! Report back. Pictures are preferable.