Ozu Castle, a historic castle located in Ehime Prefecture, has a secret: This is the only castle In Japan where you can stay overnight to experience the rich history of this castle. While coming with a price tag that definitely is more on the high end, this will be one of the most memorable stays of your life including various cultural activities during your stay.

https://castlestay.ozucastle.com/en/home

If you don't have the time or budget to stay, you will pass it very slowly if you take the Shikoku sightseeing train Iyonada Monogatari on your way to Yawatahama or back to Matsuyama.