I've only been to Himeji once. I was there for two days, but I spent the entire time at the historic Himeji castle so I didn't see anything else. The castle was amazing, considered by many the best castle in Japan. I forget the exact date I was there but it was sometime during New Years vacation. As such, almost every store was closed, so my wife and I were forced to buy convenience store food to eat for dinner and lunch. I'd like to go back one of these days and explore more.
The castle grounds did have some gardens, but nothing like what you are showing in your photos. Wow! That looks like an amazing place. Japanese gardens are really incredible, and that one no exception!
The idea of sister cities is interest. A few years ago my home state, Indiana, made an effort to attract more Japanese business to the state. I'm not sure the reasoning behind that, but it worked, and now Indiana has the second highest number of Japanese businesses in the US, around 210. Along with the businesses came a host of sister city connections. So many cities in Indiana now have sister cities in Japan and small Japanese gardens that their sister city helped build.
I'm not sure what's behind the sister city thing to be honest, I've never been that interested in the concept, but I'm certainly interested in nature and gardens and this one was a good one for sire. I can't believe I didn't know of its existence but I do now and I'll be back for sure.