Takamatsu Castle (Tamamo Kōen) 玉藻公園(高松城跡)
Moats of seawater, not river water; it is the largest sea castle in Japan.
Founded in 1590 by Ikoma Chikamasa and enlarged from 1642 by Matsudaira Yorishige, it was the centre of the Takamatsu domain for two and a half centuries. The tenshu, built by the Matsudaira in 1669, was dismantled in 1884. What remains are the Tsukimi turret, the water gate, the covered gallery and a corner turret, Important Cultural Properties since 1947; the Hiun-kaku building, the former Matsudaira residence, has been one since 2012, and its garden has been a national Place of Scenic Beauty since 2013. It is castle number 77 of the 100 Famous Castles of Japan (since 2006).
Kagawa
Takamatsu-Chikko, Takamatsu
https://theanimetrip.com/luoghi/castello-di-takamatsu-tamamo-koen