Once again [link] Nijou Castle, built between 1601 and 1626 by order of the shogun Tokugawa Ieyasu, now a UNESCO World Heritage Site.
I love how the whole building blends in with the surrounding gardens and doesn't stand out above the trees. Most traditional Japanese buildings have very sober interiors, but this castle is the exception to the rule: the ceiling is covered in elaborate flower designs, all sliding doors are hand painted...it's a real pity you aren't allowed to take photos inside.
Also, this castle has many interesting features such as:
(From Wikipedia)
One of the most striking features of the Ninomaru Palace are the "nightingale floors" (uguisubari) in the corridors. To protect the occupants from sneak attacks and assassins, the builders constructed the floors of the corridors in such a way as to squeak like birds when anyone walks on them.
Some of the rooms in the castle also contained special doors where the shogun's bodyguard could come out and protect him.
(I can tell you the space behind those special doors where the bodyguard hid were more like wardrobes that actual rooms)