Inokashira Park is in Kichijoji. It is especially famous for the cherry blossoms around the lake, but it is beautiful in all seasons. It was originally a shogunal park, then became the property of the emperor, then was given to Tokyo Metropolis.
Boats can be rented for rowing or paddling on the lake, there is also a small zoo which has a water-bird section. Nearby is the Studio Ghibli Museum, a must for all interested in anime.
Kichijoji is the transfer point between the Inogashira Line, which goes to Shibuya, and the JR Chuo Line, which takes people to the western part of Tokyo. If you take this route, why not get off one stop before Kichijoji, Inokashira Koen Station, and walk through the park to Kichijoji Station?