Tokyo was originally a castle town centered on Edo Castle during the Edo Period(1603-1868). Edo is the old name of Tokyo, and succesive Tokugawa Shoguns ruled Japan from the castle. Edo Castle site was changed into the Imperial Palace Grounds in 1869 soon after Emperor Meiji(1852-1912) moved to Tokyo from Kyoto which was the capital of Japan for about 1,000 years.  

That used to be the main gate to Edo Castle. Now one of three gates to the East Gardens of the Imperial Palace which is the popular sights for tourists. We need at least one hour walk to get around in the garden.

That old long wooden building is one of three guard houses for security which was the second check point and many samurai were around the clock in the building to keep watch. From the place, we are walking upwards towards the core of the castle.  

We are walking on the slope approaching the core of the castle. On the way, as we see the center of the photo, S-curve was set for the defending purpose because the castle was an impregnable fortress. 

We have got to the place where there used to be a large wooden building of a main office of samurai called Honmaru of the castle. A little faraway, a diagonal shaped stone walls is seen. That was the foundation stones for the main tower of the castle but the main tower was destroyed by the Great Fire more than 350 years ago. 
There are many things to talk to you about the castle-related story while walking and seeing. I wait for you to join our tour.