Kyu-Furukawa Gardens

Kyu-Furukawa Gardens, or Kyu-Furukawa Teien (旧古河庭園), now a public garden, was a residence of Furukawa family who owned Furukawa Zaibatsu (conglomerate) until the end of WWII. This place was at first a villa of a prominent politician but was obtained by Furukawa family, and it was after that that it became what it looks like now. Its entrance is on the north side of the garden.
This site is designated as a Place of Scenic Beauty. The Western-style house building, together with a Western-style garden, was completed in 1917. Both were designed by Josiah Conder, a British architect famous in Japan. Its Japanese garden, which was designed by Ueji, a well-known garden designer from Kyoto, was also finished in the same year. The Western-style garden is a rose garden, and in spring and fall, the Rose Festivals are held.
If you're to visit this site, visit Muryoji Temple also. Muryoji is a Buddhist temple with a beautiful garden, and is almost adjacent to Kyu-Furukawa Gardens.
This site is a 6-min walk from Tokyo Metro Namboku Line Nishigahara Station, or a 6-min walk from JR Keihin-Tohoku Line Kaminakazato Station.

Rose Festival

During the Spring Rose Festival (but not during the autumn one), there are some days when this site gets open until 9PM, and in this period the gardens are illuminated ethereally.