British artist Jason de Caires Taylor creates an underwater sculpture park in the West Indies, not only to "explore the boundaries between art and the environment" but also to portray a beautiful process that happens to be doing nice things for the ecosystem. You can see a video of the sculptures on YouTube.
The Site of Reversible Destiny is an "experience park" conceived on the theme of encountering the unexpected. By guiding visitors through various unexpected experiences as they walk through its component areas, the Site offers them opportunities to rethink their physical and spiritual orientation to the world. [via]
The Imaginary World "began as an idea to create a fictional theme park. I would create models, drawings, souvenirs, etc to build an entirely fictional place. As the idea grew I created characters to inhabit the park and some of these characters took on lives of their own that went outside the boundaries of the park." found via Andy Partridge
Guerrilla art appeared at Magnuson Park's Kite Hill in Seattle again. This time, a war message, it seems.