The Miyakoshi's house is a very old building located in Oppetsu, Nakadomari-cho.

The Miyakoshi family's elegant house annex "Shimu-an" and the garden "Seisen-en", which is a fusion of ancient and modern garden designs, were given by the then head of the family, Masaharu, to his wife Iwa on her 33rd birthday in 1919. 

The fittings and furnishings of the Shimu-an are lavish, its three windows most notably are decorated by stained glass artist Ogawa Sanchi, who relied on a large budget to create them. 

These stained glass works are regarded as Sanchi's masterpieces because of their skillful incorporation of traditional Japanese design while still being aware of the design trends of the time, and also because they incorporated cutting-edge glass technology at the time. 

Seisen-en is known as a famous garden that was visited in 1926 by Kenzo Adachi, the Minister of Communications. It was one of the largest gardens in the prefecture during the Taisho era (1912-1926), and once contained a tea ceremony house. 

Surrounding the Shimu-an are three different types of gardens: the Oishi Bugaku-style garden, the Karesansui garden, and the Ikeizumi garden, all of which allow visitors to enjoy the seasonal scenery. 

In December 2008, the Miyakoshi House Annex was designated as a town tangible cultural property (building), and the Miyakoshi House Garden was designated as a town memorial (scenic beauty). 

Open to the public: May 29 to June 27, 2021, also to be opened in August.