Hagi Castle was built in the early 1600s as the Mori clan's seat after their defeat at Sekigahara. The keep is gone, dismantled in the Meiji period, but the moat, stone walls, and setting below Mount Shizuki still give the site a clear outline.
It is best treated as part of the wider castle-town walk rather than a standalone castle visit. In plum or cherry blossom season, the park earns extra time.