Grace had written recently about Reigando. Here is a further suggestion most useful for people who have access to a car.
There is a network of hiking trails called the “Kyushu Shizen Hodou” (九州自然歩道), one of which passes over Mt. Kimpo. If you park your car at the mountain top and find the trail (it branches from the service road to the summit), it will take you down to the labyrinth of the mountain’s west-facing mikan orchards - and from there, you’re on your own, but pretty much every tiny road or path will bring you to Reigando. If you’re lucky, you’ll find one of the shacks that contain the conveyor-belt devices that separate mikan by size. And don’t feel shy about sampling the fruit from the trees - the farmers really don’t care (in fact, they’re likely to give you a free bagful if you ask - but that would mean you’d have to lug that back up the mountain when you return.)
It’s not an easy hike, but my kids used to do it as elementary school students. Bring supplies (liquid!), as there are zero stores (though plenty of mikan), and a camera as the views are breathtaking. - William