Tokyo, Kyoto, Hiroshima, and -- ???

Hi all, I'm planning my 2nd trip to Japan. The first time I went was with a tour group and we did Tokyo, Kyoto, Kanazawa, Hiroshima and Osaka. I'm planning a 2 week trip for this October with my mom, who has never been to Japan.

We're doing Tokyo, Kyoto, and Hiroshima for sure. I'm looking for a 4th city to spend 3 days at. Can't be Kanazawa or Osaka. I can't even really describe what specifically we're looking for. Touristy things are fine. I like nature, food, and events/exhibits I can't see in the US. Open to any suggestions.

Thanks :)