“The Fifth Aso Energetic Walk 2015”
The event will be held on the 5th and 6th of September and you need to apply by August 14th. The web site is mostly in Japanese so if you are interested and unable to make sense of the interface, you might want to ask someone for some help.
http://www.city.aso.kumamoto.jp/static/sightseeing/event/asowalk/