One of my favourites too.

"Today is international park(ing) day, when activists reclaim parking
spaces and turn them into mini green parks.

Hooray, one of my favourite days of the year: International Park(ing)
day. This glorious anti-car festival only started in 2005, when a San
Francisco-based group called REBAR decided that they would take over a
parking space for a day and turn it into a park. So they did.

They brought along some astroturf and a bench and a tree and fed the
metre all day long and had a lovely day with people asking what they
were doing and why. As one of their members explained, they re-
interpreted a parking space as a potential inexpensive short-term
lease, and decided that it didn't just have to be for cars: the day
was a success.

But it didn't stop there. People wanted to know how they could do it
for themselves. REBAR explained the basic principle (don't forget to
feed the metre - that's it really) and set up a website where people
could post up pix. By the following year REBAR had a partner (the
agreeable Trust for Public Land) and every year since then it's just
got bigger and bigger, spreading all the way around the world, to
Italy, Germany and Australia (in the YouTube clip above)..."

More:

http://www.guardian.co.uk/environment/blog/2008/sep/19/activists