Kyu-Iwasakitei Gardens (旧岩崎邸庭園), now a public garden, was the main residence of the Iwasaki family until the end of WWII. Kyu-Iwasaki-tei means "former Iwasaki house". The Iwasaki family was the owner of the Mitsubishi Zaibatsu (conglomerate) in those days, and the grounds of this mansion were three times larger than it is now.
Now only three buildings remain, and all of them are designated as Important Cultural Properties. As is often the case with the premises of a Zaibatsu owner family, this residence has a Japanese-style house which they used for the main part of their daily life and a Western-style house whose principal purpose was to welcome guests.
As for its garden, although it bears the word "Gardens" in its present name, most part of what it used to be is now lost.
This site is near Ueno Park, and is three minutes away from Yushima Station of the Tokyo Metro Chiyoda Line.
The Western-style mansion was built in 1896. It was designed by British architect Josiah Conder, who is pretty famous in Japan.
The Japanese-style house was also completed in 1896. It used to be much larger than it is now but most of it was destroyed after WWII to build a governmental facility.
The Billiard house, which was designed by Conder, was constructed in 1896 as well.
Located around Kyu-Iwasakitei Gardens are Ueno Park, Yushima Tenjin Shrine, Rinshoin Temple, and the Hongo Campus of Tokyo University.