About 20 minutes "on foot" from Tokyo Terminal (Marunouchi Exit).
If you come from other places by a subway, the nearest station: Harajyuku (JR line)
or Nijubashimae (Chiyoda line C10) or Otemachi (Marunouchi Line (M18) Tozai Line (T09) Chiyoda Line (C11) Hanzomon Line (Z08)
The Imperial Palace (Kōkyo, literally "Imperial Residence") is the primary residence of the Emperor of Japan. It is a large area located almost in the center of Tokyo and contains buildings including the main palace, the private residences of the Imperial Family, an archive, museums and administrative offices.
It was built on the site of the old Edo Castle. The total area including some gardens such as the Outer and East Gardens is 3.41 square kilometers (1.32 sq mi). The East Garden of the Imperial Palace is one of the remains of Tokugawa Shogunate Government Edo castle. It was open to public in 1968, covering an area of approximately 0.21 square kilometers. There are the remains of Edo Castle such as the gate, the guard house and Tenshudai (Remains of the main tower) as well as a typical Japanese garden.
Nippon PLUS offers some selections to visit the Outer Garden or the East Garden of the Imperial Palace and nearby places. You can request an original tour there too.