How about an outdoor festival pavilion -
the Auerworld Palace? It was designed by Marcel Kalberer and built/planted in 1998 with the help of 300 volunteers.
Most of the website text is in German, but it has lots of photos of other "Living Architecture" projects throughout Europe. Reading through the website it appears that Sanfte Strukturen (an architecture studio) uses bundled willow branches that are lashed together to form the structure. The willow bundles then sprout and then grow out over time.
More Auerworld Palace info and photos here -
Auerworld Palace | Auerstedt, Germany | Atlas Obscura