Edo Castle is a flatland castle build in 1457. Now it is part of the Tokyo Imperial Palace (where the Emperor and Emperess live) in Tokyo, which was formerly known as Edo. Tokugawa Ieyasu established the Tokugawa shogunate here and it functioned as the military capital during the Edo period. It became the Tokyo Imperial Palace during the Meiji Restoration.
I was happy to visit the area, but I didn't see the Imperial family while I was there.
(If you are interested in Japanese Castles, check out my Castle Page to see the castles I've visited.)