Basically, newer stone walls use more processed stones. However, in the case of those in Nakatsu Castle, it looks like it is the other way around.
Yoshitaka Kuroda, who built Nakatsu Castle, is known to many Japanese people as the military strategist of Hideyoshi Toyotomi. However, he was actually a working general and a secretary under Hideyoshi.
中津城を築いた黒田孝高(官兵衛、如水)には豊臣秀吉の軍師であったという印象があるでしょう。しかし実際には秀吉の下、現場で働く武将で、かつ秀吉の秘書官のような存在であったようです。
A big event for the Hitoyoshi area happened in 1877, when a hero of the restoration, Takamori Saigo started a rebellion against the government known as the Seinan War.
The supply of the water from the Kumagawa River provides specialties such as hot spring, Kuma-shochu spirit, and sweet fish while the water could sometimes cause flood damages.
The early stage of Hitoyoshi Castle was much larger than its later stage during the Edo Period which is what we call the castle ruins.
The only thing I would ask the city to improve on the castle would be to open the views from the Main and Second Enclosures.
I recommend using a detour route to the castle through the former Kishu Road and castle town. This is because you can understand how the castle and town were developed by seeing them.