Japan is composed of a spine of volcanoes extending from the sea south of Kagoshima to northern Honshu. This is due to complicated interactions between the Pacific, Philippine, North American, and Eurasian plates upon which Japan floats. Mount Kimpo is a granite monolith located just south of the castle - in fact, it is where the castle’s rocks were quarried. It is a dormant volcano - imagine if it erupted again! - lying between the active Unzen and Aso volcanoes. Sort of like a mini-Aso, it has a caldera which is heavily cultivated with grapes and citrus. Now is a good time to visit. You can take a bus from Kotsu Center to Touge Pass　(Tougenochaya Kouen - 峠の茶屋公園) and then hike to the peak from there - it is a most pleasant walk. The view from night is particularly spectacular. - William