This interactive art project by artist Olafur Eliasson is one of the most engaging we've seen. It starts as thousands of white Lego blocks dumped onto a series of tables...
...which passers-by assemble into fantastic structures.
Some play off one another.
And others involve destruction or modification of others' work.
We like art that gets people thinking about their role in the city, so while the project isn't screaming about green, there is a subtle message: if regular people can create and recreate art, then regular people can recreate the city, too.
These pictures are from Copenhagen, and you can read more about the project here. Has it come to your city?