Traveling long term in Japan

I am currently in Japan and have been for about 2-3 weeks. I have been to Tokyo, Osaka, and visited Kyoto and Nara while in Osaka. I have months left of time to travel before I start school again but I do not know where to go. I thought about going to Fukuoka and then making my way up the country going to smaller cities etc but I just don't know.

I think I want to choose a place and stay there for a month or so just to relax and fully enjoy living in japan. I don't want to stay in a super big city like tokyo or osaka. I guess my goal would be to stay in a decent town/city that has a lot of nature and some fun things to do like restaurants/bars/cafes. I love hiking and nature so this is also a priority for me. Does anyone have any recommendations?

There are just so many options I just don't know where to go or start.