The Adventure Playground at the Berkeley Marina has been a famous and very much creatively evolving landmark for kids and their families in the Bay Area, California for over 30 years. The kids themselves design, build and continually create the playground in which they play (with minimal supervision from staff) using repurposed materials such as old pianos, boats, wood, and tires.

Ride the zip line or hammer, saw, and paint.

Build forts, towers, boats, musical instruments...

As the website says, these low risk, high reward activities create opportunities for young people to learn cooperation, meet physical challenges, gain self confidence and take more ownership of their own creative learning and environment.

The Adventure Playground seems countercultural now compared to the many sterile, smooth, and 'safe' plastic playgrounds that are largely a by product of a series of legal actions / litigations to create "safe" and "risk-free" environments. 

From the website:

"The concept for Adventure Playgrounds originated in Europe after World War II, where a playground designer studied children playing in the "normal" asphalt and cement playgrounds. He found that they preferred playing in dirt and lumber from the post war rubble. He realized that children had the most fun designing and building their own equipment and manipulating their environment. The formula for Adventure Playgrounds includes Earth, fire, water, and lots of creative materials..."