Originally Posted by
FlyerBeek
Personally, I think 3 nights would be perfect at the IC Beppu if just limiting your visit to Oita Prefecture. Don't think I would recommend anything more than that. If you've got a car and enjoy onsens, I would highly recommend visiting Yufuin as well. If wanting to hop on the train from Beppu - you can rent a car at OIT airport and drop-off at either the Beppu or Oita stations. If going up to Fukuoka (about 2hr20min train ride) - highly recommend splurging for the Sonic (Series 883) Green Car! Kyushu is a fantastic island to explore by train:
https://www.jrkyushu.co.jp/english/.
-FlyerBeek
Good points. If he's a big spender, he might even consider taking the Seven Stars train around Kyushu but he'd have to apply well in advance because it's a lottery system. It has routes that pass through Beppu, Oita, and Yufuin, and several other Kyushu cities.
https://www.cruisetrain-sevenstars.jp/english/