Himeji is a city in Hyogo Prefecture, about 90 minutes west of Osaka by Shinkansen, and it has one of the finest castles in Japan. Himeji Castle — also called White Heron Castle for its gleaming white plaster walls — is a UNESCO World Heritage site and one of only twelve original castles in the country to have survived intact, never destroyed or rebuilt.
The castle sits on a hill visible from the Shinkansen tracks as you pull into the station. Walk straight down Otemae-dori for about 15 minutes to reach it, or take the Miyuki-dori arcade running parallel if the weather turns. The grounds are extensive and worth taking slowly; the main keep rises six storeys and the view from the top over the city and surrounding plain is excellent.
The Koko-en garden, reconstructed in the Edo period style just next to the castle grounds, makes a pleasant addition to the visit. Allow at least half a day for both. If you have a full day, the mountain temple of Engyo-ji on Mount Shosha — the Last Samurai filming location — is the obvious second stop.