The building consists of a main hall built as a three-storey English Tudor-style villa which was completed by a businessman Shotaro KAGA in 1932, and an adjacent newer building underground called 'Underground Jewelry Box' which is a modern piece of architecture designed by Tadao ANDO.
建物は実業家・加賀正太郎が1932年の昭和初期に完成させた三階建てのイギリス・チューダー様式の山荘である本館と、それとは別に隣接して地下に作られた安藤忠雄設計の現代建築の新館「地中の宝石箱」からなる。