Nagoya Castle, Japan’s first castle designated as a National Treasure, is in Aichi Prefecture, roughly halfway between Tokyo and Kyoto. 
A brief bit of history: The castle, built under the orders of Tokugawa Ieyasu, was completed in 1612. It was built to secure an important position on the Tokaido Road to ward off attacks coming from the Osaka area. The Tokaido Road was one of the major roads that connected Tokyo to Kyoto and Osaka. As a side note, women were not allowed to travel alone on the Tokaido Road. They had to be escorted by a man.
During World War II, the castle was used as the Tokai District Headquarters and Administrative Office for the Nagoya POW Camp. Most of the buildings, including the main palace were burned during the air raids in May 1945. Once the Japanese knew that Japan’s mainland began being threatened, most of Nagoya Castle’s sliding doors and paintings were put in storage to protect them (they had been designated as National Treasures in June 1942). From what I saw, thanks to this, at least some of the sliding doors and paintings were saved. The castle is still currently under reconstruction.
Usually I am not a big fan of the interior of reconstructed castles, but Nagoya Castle is an exception. The interior has been redone fantastically. There are tons of displays, notes on history, and even part of one floor that has been built to make you feel like you are walking through an old Japanese town.
A 3D map of what the original Nagoya Castle and village looked like
A katana (sword) on display. Swords are treated with great respect in Japan. It is said that the sword holds the soul of the samurai.
On the left, one of the sliding screens. Above, a sword’s “tsuba”, or sword gaurd.
A palanquin on display
Part of the part of the castle that has been remodeled to look like an old town
A recreated bookshop
Tasty? Replicas of some dishes that would have been served at fancy meals
The view across Nagoya from the top floor of the castle
Many feudal lords helped with the construction the castle’s walls. Each of them engraved their marks on the stones they moved so as to distinguish their stones from other feudal lord’s
One of the most closely associated things with Nagoya Castle are the kinsachi, or golden dolphins that adorn the castle’s roof. They are a symbol of the feudal lord’s power. 
