In the early Edo period, the first Tokugawa shogun, Ieyasu, stripped all power from Kyoto's Imperial Court by consolidating a new military and political center at his far-off fortress in Tokyo. Nijo Castle, begun in 1603, is a grandiose and unequivocal statement of the shogunate's power. Nijo-jo's wide exterior moat and towering walls are the castle's exterior face, but once inside a second moat and defensive wall become visible. This had less to do with defense than it did with reinforcing the castle's social statement: access to the inner sanctum depended on a visitor's status within the shogunate's hierarchy, and the powers-that-be could remind anyone of their place in the system. Anyone who was permitted inside was as much a hostage as a guest, a feeling surely driven home by the castle's ingenious nightingale floors, which "sing" as you walk across them, revealing your movements at all times. (You can see how they work by looking underneath the balcony as you walk through the garden.)
Tokugawa shoguns were rarely in Kyoto. Ieyasu stayed in the castle three times; the second shogun stayed twice, including the time in 1626 when Emperor Gomizuno-o was granted an audience. After that, for the next 224 years, no Tokugawa shogun visited Kyoto, and the castle started to fall into disrepair. Only when the Tokugawa shogunate was under pressure from a failing economy did the 14th shogun, Tokugawa Iemochi (1846-66), come to Kyoto to confer with the Emperor. The 15th and last Tokugawa shogun, Yoshinobu, famously returned power to the Emperor in 1867, the central event of the Meiji Restoration. Since 1939, the castle has belonged to the city of Kyoto, and considerable restoration has taken place.
You can explore Nijo-jo at your own pace, and handy audio guides give great explanations of what you're seeing. Entry is through the impressive Kara-mon gate, whose sharp angles are intended to slow an attack. The path from the Kara-mon leads to the Ni-no-maru Palace, whose five buildings are divided into various smaller chambers. Inside the central hall, costumed mannequins are frozen in the Tokugawa shogunate's dying moment, returning the government to the Emperor. The impressive garden was created by landscape designer Enshu Kobori shortly before Emperor Gomizuno-o's visit in 1626. Crane- and tortoise-shape islands symbolize strength and longevity. You can get to the castle via Tozai subway or Bus 9, 12, 50, or 101 to Nijo-jo-mae.
Horikawa Nishi-iru, Nijo-dori, Kyōto, 604-8301, Japan