Koyama Garden is adjacent to Toshimaen and has a Japanese garden centered around a pond. The garden design takes advantage of the height difference of the original land and a tea room in the center of a tiny peninsula. In the early Showa period, this land was the residence of Tasuku Egi, a politician who served as the Minister of Justice and the Minister of Railways. Prior to then the area around Toshimaen and this garden was where Nerima Castle (which ruled this area at that time) was located. The park was opened in the latter half of the Showa period, but in recent years both the building and the garden have been completely renovated and open to the public.