Takasugi-an, Japan [huanqiu.com]
Takasugi-an literally translates as "a teahouse [built] too high." Located in Nagano, Japan, the teahouse was built atop two chestnut trees, cut from a nearby mountain and transported to the site. Architect Terunobu Fujimori designed and built this single-room structure for his own use. It is accessible only by free-standing ladders propped up against one of the trees and features an interior covered with plaster and bamboo mats.