Japanese castles provide the same witness to history as ancient documents. Understanding the castle and its location gives you an idea of the history of Japan as well as the history of military tactics. The donjon (castle keep) is the icon of a Japanese castle.
The photos in this audio segment are of Hiroshima castle. Unfortunately, this castle was destroyed by the blast of an atomic bomb in 1945. You can visit the oldest existing castle with a trip to Inuyama castle. I lived near this castle for 10 years and enjoyed great views of it.
This website illustrations are truly awesome. https://inuyamajo.jp/learn/donjon/