I went to Himeji castle last weekend.
The main tower is still under construction, so you can't enter that particular building until next year. But the castle is very large and there are many other parts of the building you can go into.
It is a beautiful castle, that has received a lot of attention recently due to the current taiga drama about Kuroda Kanbe. There is a small NHK drama museum just in front of the castle where you can see lots of props and costumes from the TV show.
(I recommend you check out this museum first because they give you a coupon book at the end which will give you a discount on some local restaurants and your castle entry fee.)