Carsten Holler creates some great, interactive spaces well-worth checking out - here are some images from a 2006 exhibition in Turbine Hall in London that relate to the Playground project. I also recommend digging through his website and looking at some of his other past projects for reference.

He also has a review of a recent project in January's Art In America that would be worth looking at.

Katamari Damacy game designer Keita Takahashi announced as designer for children's playground in Nottingham City
A link to his blog charting progress on development of the site can be found here

Children's Playground, Takino Hillside Park

Designer:  Fumiaki Takano

While the Miniatur Wunderland is a simply a model train display, there is nothing simple about it - a great reference for anyone interested in narratives, modeling, kinetics, installation, exhibition display and computer controlled interfaces.

This is a project I came across recently that piqued my interest that I thought I would share.
With regard to mixing or multiplying purposes, consider how the process of play also informs in this project - what are some other ways information can be built into the design and use of the the playground? For more information, click on the link here - Weaving Forest

The design group that created this project is a Shanghai-based group by the name of SuperNature and a link to their site can be found here.