Many seem interested in Kirk’s post regarding Takachiho, so I thought to add a bit more information.
Takachiho Gorge was carved out of rock deposited by two different Aso eruptions, respectively 120,000 and 90,000 years ago. A close look at the photographs clearly show rock of two different types lining the gorge walls, the lower having crystallized into pillar formations and the upper volcanic tuft. https://ja.wikipedia.org/wiki/%E9%AB%98%E5%8D%83%E7%A9%82%E5%B3%A1
Access is possible by bus, the Sanko Tokyu Takachio-go which departs from platform 3 at Kotsu Center once daily at 9:11 and arrives at Takachiho at 12:43; the return bus departs Takachiho at 16:41 and arrives around 20:00. Round-trip tickets cost 4,110 yen. Given the time constraints, an overnight trip would be best. Here is a PDF of the timetable: http://www.kyusanko.co.jp/sankobus_top/sites/all/themes/SankobusTop/pdf/20160708takachiho.pdf and the route Website: http://www.kyusanko.co.jp/sankobus/toshikan/takachiho/ Once there, a town bus which tours all of the main sites can be accessed all day for 600 yen. Boats can be rented for 2,000 yen/hour. This is the town tourist Website, which contains much valuable info but is only in Japanese: http://takachiho-kanko.info/
