Another place to visit if you have a car during GW (or any season) is Kurokawa Onsen, on the border between Kumamoto and Oita. There are a multitude of onsen, including one in a cave, It's said to be the inspiration behind many Miyazak Hayaoi films. You can buy a pass that lets you visit multiple inns, walking around cobblestoned streets in yukata, eating eggs boiled by onsen water. My wife had fertility problems, but a visit to the onsen solved that (we have two children now). It's healthy and very scenic. - William