That tour is conducted by the Imperial Household Agency. I went with my guests to join the tour once and did it alone once for my pleasure. It is interesting.  

Here we are at the foot of Fujimi Yagura which literally means "A watch tower of viewing Mt. Fuji".

That is the Palace. Twice a year, on the Emperor's birthday on February 23, and on January 2, the Imperial Family appear on the balcony of the building when the Emperor delivers his short address and the Imperial Family members wave greetings to the people. Those occasions are visits of the general public to the Palace. At that time, the general public(including other nationals) cross the moat on "Double Bridge", Nijyu-Bashi in Japanese. Those are rare opportunities. 

Here we are on the iron bridge of "Double Bridge", Nijyu-Bashi in Japanese. New ambassadors riding a horse-carriage cross the moat on the bridge to present credentials to the Emperor. 

That is the Imperial Household Agency building built in 1935.