Twenty years ago, 11,000 people planted 11,000 trees on an artificial mountain near Ylöjärvi, Finland. The trees were planted in a mathematical pattern based on the golden section; in time they will grow into a virgin forest each tree of which has a designated custodian. The trees can change ownership, but they can never be removed from the forest, and the mountain itself can never be owned or sold.
Artist Agnes Denes conceived the project in 1982, and the Finnish government undertook it 10 years later. The site is legally protected for the next 400 years.