In 1982, the conceptual artist Agnes Denes set out to make a mountain. After a decade of work, she made it happen. In 1992, the Finnish government announced that it would sponsor Denes’s Tree Mountain—a 125-foot-tall manmade mountain built on top of a former gravel pit, designed to serve as part time capsule, part ecological recovery project.

Tree Mountain — A Living Time Capsule was constructed on the site of a former gravel pit near Ylöjärvi, Finland between 1992 and 1996. The artificially constructed landmass stands 125 feet tall, almost 1400 feet long, and more than 885 feet wide. (The top image of the triptych above shows the mountain in 1992 and the bottom image in 2013.) The forest planted on it forms a precise mathematical pattern Agnes designed based on the golden ratio-derived spirals of sunflowers and pineapples. From above, the oval mountain looks like a giant fingerprint made up of whorls of trees.

The project was never intended to just be aesthetically pleasing. Envisioned as a way to rehab land destroyed by mining, the trees are meant to develop undisturbed for 400 years, creating what will eventually be an Old Growth forest that can reduce erosion, provide wildlife habitats, and boost oxygen production.

And it was a communal effort. The roughly 11,000 pine trees were planted by different individuals who then became the custodians of those trees. Each received a certificate declaring their ownership for the project’s full term of 400 years. They can pass along this ownership to their descendants or to others for as many as 20 generations. These custodians (which include former UK prime minister John Major and former Icelandic president Vigdís Finnbogadóttir) are even allowed to be buried under their trees. But the trees can never be moved, and the mountain itself can’t be owned or sold off for those 400 years.

Tree Mountain - A Living Time Capsule - 11,000 Trees, 11,000 People, 400 Years (Triptych) 1992-1996, 1992/2013Copyright Agnes Denes, courtesy Leslie Tonkonow Artworks + Projects, New York

“Tree Mountain is the largest monument on earth that is international in scope, unparalleled in duration, and not dedicated to the human ego, but to benefit future generations with a meaningful legacy,” Denes writes. It “affirms humanity's commitment to the future well being of ecological, social and cultural life on the planet.”