The Imperial Palace is such a vast place with many trees that you cannot have a glimpse of the Imperial Residence near the Hanzomon.
It differs from Buckingham Palace that the Residential area and the surroundings are completely off limits.
There is a free guided tour held by the Imperial Household Agency which requires nearly two hours, including the waiting time.
You're supposed to move in a group of 200 or so together, not allowed to leave in the middle, only seeing the buildings from the outside.
You won't see any gorgeous chairs or anything, which you could see when you visit the Bleinheim Palace or the State Guest Houses in Yotsuya.
If you're interested in the Imperial Palace tour, please read below for the details:
The tour is led by a Imperial Police Guard in Japanese.
The agency recommends you download an application software for explanition for other languages.
There are also audio devices you can ask to borrow after you go into the Soumeikan, the building you're supposed to wait till the tour starts. I didn't notice any announcement about it when I joined the tour this January, but I knew about it because I also went there last March. Oh, it is written on your numbered ticket, anyway.:-)
Download the application or borrow the audio device. Without them, it might be a torture unless you understand Japanese Language.
Of course, you can hire me and I will explain in English, however the Japanese announcement would be quite loud.
The historical site which made Tokyo great is not this area, but the East Gardens, even though not many buildings remain, because the wooden buildings have been burnt down more than hundred and fifty years ago.