Now these are the ultimate tree houses. Living trees are guided into the shapes of towers, cathedrals, and pavilions, creating wooden structures that continue to grow and bud and bloom.

Vegetal Cathedral (La Cattedrale Vegetale), designed by Guiliano Mauri, grounded in 2001, completed in 2010, in the woods of the Sella Valley, Trentino, North Italy. It stands on an area of 7,000 sq ft (650 sqm) and 16-70 ft (4.9 to 21.3 m) high.

(via Ubuntu and Alessandro)

At 170 ft (52 m) long, the world's largest living structure named Weidendom (Willow Chapel), Rostock, Gemrany, 2001, by Sanfte Strukturen

(via Grillsportverein, Weidendom, Schiwago and Arge Naturschutz)

Another Weidendom, Schlepzig, Germany, designed by Marcel Kalberer, built in 2004.

(via Spreewald Brauerei)

The tree-shaping system named Botany Building, which enables pavilions and other organic structures from willows or other quick-growing trees to be built. The system was developed by Oliver Storz, Ferdinand Ludwig and Hannes Schwertfeger at the University of Stuttgart, Germany, 2009

After the trees grew for a few years, the support structure could be removed.

(via Designboom)

Na Hale 'Eo Walawi, by Patrick Dougherty, in The Contemporary Art Museum, Honolulu, Hawaii, 2003

(via Stickwork)

The first tower made entirely out of living trees (white willow) with the Botany Building system mentioned above, built in 2009.

The support structure will be taken down after 8-10 years, if the willow could hold all three zinc-coated platforms.

(via Inhabitat)

Just Around the Corner by Patrick Dougherty, New Harmony Gallery, New Harmony, Indiana, 2003

(via Stickwork)

The Auerworld Palace in Auerstedt, Germany, built in 1998 by 300 volunteers from all offer the world, designed by Marcel Karberer and Sanfte Strukturen

(via tin.G and Sanfte Strukturen)

Simple Pleasures, Bowdoin College Museum of Art, by Patrick Dougherty, Brunswick, Maine, 2001

(via Stickwork)

The Patient Gardener, a two-story retreat consisting of ten Japanese cherry trees, created by visiondivision, Politecnico di Milano, Milan, Italy, 2011. The final result can be enjoyed around 2090.

(via Archiscene)

Bonus: The Green Cathedral, a land art project of 178 Lombardy poplars mimics the shape and size of the Cathedral of Notre-Dame, Reims, France, located near Almere, The Netherlands, planted by Marinus Boezem in April 1987.

(via RogAir and Google Maps)