There is a festival on 19th of August in Uchinomaki, Aso!
There will be free entry to hot springs and a fireworks show. Each company/group will do the bonodori dance. The B.O.E. usually participates every year and they change their colours too. The hospital workers will wear green happi coats, the city hall will wear purple, the firemen will wear red etc. The food stalls are awesome!
See the blog post below for more details (in English and Japanese)