Source: http://commons.wikimedia.org/wiki/File:Marunouchi_Area_from_Tokyo_Tower.jpg Author: Chris 73
Marunouchi is the central business district of Tokyo, located in Chiyoda ward. The name Marunouchi means "inside the circle", and refers to its located within the inner moat of the Imperial Palace.
The Marunouchi District can be considered the nerve-center of Japan. Three of the country's biggest banks have their headquarters here and a quarter of Japan's GDP is generated from here. Until 1592, what is today Marunouchi was sea - part of Edo Bay - until the sea was reclaimed and turned to land. Today Marunouchi comprises neatly lined office blocks and high-rises.
Marunouchi is the nerve-center of Japan, and Tokyo Station is its throbbing heart. Located on the east side of Chiyoda ward, the station is the terminus of the Shinkansen bullet trains from all over the country.
By Subway
While many subway lines crisscross Marunouchi District, only the Marunouchi Line (M-17) stops at Tokyo Station.
Tokyo Station, Marunouchi side
Source: http://commons.wikimedia.org/wiki/File:Tokyo_Station_Marunouchi_side.jpg Author: Chris 73
What to see in Marunouchi
Imperial Palace Official residence of the Emperor of Japan.
Tokyo Station The main intercity rail terminal of Tokyo.