Located on the outskirts of Bergamo, at the foot of Monte Arena, the Tree cathedral, created by Italian artist Giuliano Mauri, is one of the world's most impressive examples of organic architecture. In 2001, his love for nature inspired him to draw up the plans for a project that took his art to a whole new level and left the people of Bergamo stunned – a cathedral made only of trees. Unfortunately, Mauri died unexpectedly in 2009 and never got to see his grand plan come to life, but as an homage to his life's work, the project was initiated in 2010, the International Year of Biodiversity.

The frame of the tree cathedral consists of 42 columns made with fir trunks, with branches of chestnuts and hazelnuts forming support structures around the young trees. With time, they will grow stronger and the wooden structures will slowly deteriorate, offering a seamless transition from a man-made structure to a completely natural creation. Right now the 6,000 meters of supporting branches around the 1,800 fir trees are held together with nails and string, but as the beeches grow, they will wither away and eventually be dismantled.