Most of Japanese castles consist of rings of defense with three circles, “with the honmaru, or main circle, in the center, followed by the ninomaru, the second circle, and the sannomaru, or third circle”("Castle Tower (Tenshukaku)”). These rings are all concentric, and this style of castle is called Rinkaku. They were mainly found in the centers of a town, and these towns became known as castle-towns. Many have been reconstructed due to the many wars that have gone on in the past few centuries. Most of the reconstructions were done in concrete, when the original castles were made of wood, and most are now museums. The castles have many towers that can be 2-5 levels and have many interior floors in that space, compared to the lesser amount of outdoor floors. In non modern castles, there are palaces, or Goten, which were houses for the lords, however are not used for that purpose anymore.
This image(background) is from the Kumamoto castle and is showing a Goten that is now full of art, and is found at the center, or honmaru of this castle. An image of this castle, which is in the Rinkaku style, is shown at the top of this page. https://gaijinpot.scdn3.secure.raxcdn.com/app/uploads/sites/6/2018/07/kumamoto-castle-main.jpg(castle) https://muza-chan.net/aj/poze-weblog7/fusuma-honmaru-goten-palace-kumamoto-big.jpg(goten)