City Swings is a project from two Swedish people, Akay and Pete. Made from found materials like wood, car tires, plastic milk crates and rope, Akay and Peter secretly hung 65 swings around Stockholm for everyone to use and enjoy.
These and more projects are featured in their book Urban Recreation: http://www.amazon.com/Urban-Recreation-Akay/dp/9197398179?ie=UTF8&s=books&qid=1206732703&sr=8-1
Akay and Pete
City Swings (2008)
Superused: wood, car tires, plastic milk crates and rope