It took less than an hour by train from Hiroshima so Himeji is a very day trip. Himeji is the only non-reconstructed feudal castle (there are 12). Wikipedia says it was bombed twice in WWII and one firebomb landed on the top floor but didn't explode. It's also known as the White Egret Castle. It was used in Akira Kurosawa's 1985 "Ran" film, "You only live twice" and the "Shogun" tv mini-series.
The castle was finished in 1618. One of Himeji's most important defensive elements, and perhaps its most famous, is the confusing maze of paths leading to the main keep. The gates, baileys, and outer walls of the complex are organized so as to cause an approaching force to travel in a spiral pattern around the castle on their way into the keep, facing many dead ends. This allowed the intruders to be watched and fired upon from the keep during their entire approach. However, Himeji was never attacked in this manner, and so the system remains untested.
We visited on a Sunday but it was the day before a national holiday and we ended up queuing for an hour to enter the castle. Then it was a very slow progression to the top from the sheer number of people. It's one of the most visited castles in Japan!