21 Balancoires (21 Swings) is an urban scale collective instrument, a game where together we achieve better things than separately. The installation consists of a series of 21 musical swings. When in motion, each swing triggers different notes. When used all together, the swings compose a musical piece in which certain melodies emerge only through cooperation. It's a game where, from the start, you need to adjust to the actions of others.The notes that are played are determined by how high a person swings. The color of the swing indicates the instrument it plays: piano, harp, guitar, vibraphone. The instruments are distributed differently within each set of three swings to create different musical configurations.When multiple swings move in synchronicity, a mini scale is played, revealing more notes and melodies. When all swings are in use, a secret musical mode is activated to give a special reward to players a synthesizer sound plays on all swings and transforms the experience.The result is a giant collective instrument that stimulates ownership of the space, bringing together people of all ages and backgrounds, and creating a place for playing and exchanging in the middle of the city center.