Butterfly Greenhouse, Kashihara City Museum of Insects (橿原市昆虫館 放蝶温室)

The Kashihara City Museum of Insects (Kashihara-shi Konchūkan) opened on 10 October 1989 in Kaguyama Park, on a site of about 46,000 m². It was designed by Nikken Sekkei and built by Takenaka. The team responsible for the butterfly greenhouse had also worked on the greenhouse for the Osaka flower exposition; the Kashihara greenhouse stands out for its careful control of temperature and humidity.

The museum found its audience quickly, passing one million visitors in May 1997. In 2002 its management moved from a public corporation to the city's board of education. It closed in December 2009 for a renovation costing around 300 million yen; the Agency for Cultural Affairs record credits the design of a renovation to the Naitō architectural office. The main building reopened on 1 May 2010 and the whole site on 1 June, with remodelled exhibition rooms, a new building for hands-on learning and live-insect displays, and a multipurpose plaza at the entrance. The two-millionth visitor came through the doors as early as October 2010.

The museum closed from 2 March to 31 May 2020 during the Covid-19 epidemic and reopened on 2 June. Japan's Agency for Cultural Affairs has included it in its survey of modern architectural heritage in Nara Prefecture.

The complex pairs two very different volumes. The exhibition building, in steel-reinforced concrete and steel, rises three storeys over a basement under a flat roof, with a total floor area of 2,883.84 m². The greenhouse wing, by contrast, is roofed with a continuous series of curved glass gables fanned out side by side, a silhouette that suggests a butterfly opening its wings.

The designers aimed for a three-dimensional glasshouse whose steel frame does not show from outside, and gave it close control of temperature and humidity. The interior, of about 500 m², is set to the subtropical climate of the southwestern islands of Okinawa Prefecture; the ground is shaped into gentle rises and a stream runs beside the visitor path.

The building received Nara Prefecture's design award for landscape harmony and the Hiroba award, and was chosen as one of Japan's hundred selected public buildings (Kōkyō kenchiku hyakusen).

The greenhouse holds about 500 butterflies of roughly ten species, reared on site and on view all year; the city gives a population of 500 to 800, drawn from tropical and subtropical regions and above all from Okinawa. The species it lists include the ōgomadara, ryūkyū-asagimadara, asagimadara, shiroobi-ageha and tsumabeni-chō.

About a hundred subtropical plant species make up the setting: palms, hibiscus, tokkuriyashi-modoki and nectar plants such as santanka, grown to feed the butterflies. A feeding station nicknamed the butterflies' restaurant offers them honey gathered by honeybees along with nutritional supplements.

The rest of the museum shows more than 1,000 insect and fossil specimens, as well as live insects, including beetles and stag beetles.

The greenhouse is seen as part of the museum, forming its glazed wing, alongside the rooms on insect evolution and diversity. Because its climate stays subtropical in every season, butterflies fly there in winter as well as summer, which makes it a good choice on a cold or rainy day. Allow one to two hours for the whole museum. Kaguyama Park, which surrounds the buildings, is pleasant for a walk before or after the visit, and the live-insect displays in the newer building round off the tour.