"Aye, there's the rub." Too many choices, not enough time.

Nara is a full day. It was the ancient capitol before Kyoto became capitol in the late 8th century and was pretty much centered on the spiritual aspects of the country. Many of the treasures and sites are very old. The main sites are in a large park-like area that is cool and pretty quiet and has tame deer running around begging for handouts. The temples and shrines tend to be pretty impressive and there is little of the "martial history" of Japan there. I think of it as a nice, laid back, almost relaxing day trip.

Himeji Castle is, as noted in the post above, the finest original castle built during the "warring states era" remaining in the country. It was started by a local warlord but expanded and completed into a critical defensive stronghold by Hideyoshi Toyotomi before he became the supreme regent (taiko.) A real tour of the castle and grounds takes about a half day if you climb up into the donjon and go through the various outbuildings. There is also a nice garden off to the left of the main entrance path. The walk from the station takes about 15 minutes and passes a couple of decent lunch places. I liked the little tonkatsu place on the right about half-way between the station and the castle.

If you want to make a long day, I agree with the above poster that you could combine a quick visit to Okayama in the morning with a back-track and afternoon visit to Himeji on the way back to Osaka. I think Korakuen garden would be nicer in the morning than in the heat of the afternoon. You could stop at one of the little noodle shops just outside the side (Okayama Castle-side) exit from the garden for lunch or just grab something at the station before heading to Himeji in the afternoon and then back to Osaka in the evening. Okayama Castle is pretty and nice to view from the outside but has been reconstructed and is really nothing special.

Or - just go to Nara for a cooler walking day among the really old stuff. If I had to choose just one, I'd probably go with Himeji but Nara is nice too and closer to Osaka.

JR