Shin-Edogawa Garden

Shin-Edogawa Garden (新江戸川公園) is a Japanese stroll garden located close to Chinzanso Garden. Though it is not so large and may not be attractive enough to take your time for this place alone, together with Chinzanso, it may be attractive.
In the Edo period, This garden was part of a suburban residence of Hosokawa clan, the daimyo (domain lord) who ruled major part of modern-day Kumamoto Prefecture. When the feudal times ended, this place became the main residence of the Hosokawa family. After the Second World War, it changed hands and became a public park. As for the buildings, only a study house constructed in the early 20th century is left here.
It's a 15-min walk from Tokyo Metro Yurakucho Line Edogawabashi Station, or a 5-min walk from Toden Arakawa Line Waseda Station (not to be confused with the Tokyo Metro Tozai Line's Waseda Station).

Eisei Bunko Museum

To the north of the garden, there's a small museum named Eisei Bunko (永青文庫). This building used to be the office of the Hosokawa family's residence. It now houses the collection the family possessed.
The western-style mansion the family lived in is still left farther to the north but used as a facility of an all male dormitory service for university students and is not open to the public usually.