Walk down Marunochi Naka Dori (nice atmosphere with famous brand shops) and check Marunouchi Building and Shin-Marunouchi Building which are great retail complex. Check the top floor observatory of Marunouchi Building. In Shin-Marunouchi Building, there are nice restaurants/bars on the 7th floor (called Marunouchi House) with the view of the old Tokyo Station. Also check Marunouchi Brick Square (restored 19th century red brick mansion) for nice terrace bars with the vertical garden installation by Patrick Blanc. Right near Maunouchi area there is the outer garden for the Imperial Palace. Although you can only enter once (or twice) per year, the outer garden, moat and views are excellent.
Marunouchi is the walls Street in Japan. Most of the Big company and International Bank may have their head office here. This area will never sleep as they have to liaise with other countries in Asian, Europe and America. My office is located in the heart of Marunouchi just right in front of the Red Square.
To escape the bustle of the city & relax in a landscaped Japanese garden for a moment. It's free too. Just collect your free token at the gate, don't lose it as it has to be handed bck.
A visit to Imperial Palace, NHK Studio Park and nearby Yoyogi Park will use up a whole day. Best to visit Yoyogi Park on Sunday for the street performance.