Yunotai Hotsprings Run
10k, 5k, 3k, 2k
3,000 yen for adults
1,000 yen for children
Application period: May 18 to June 17
Where: In the land of gods. Kaminokuni! Near Hakodate and Okushiri. A long way away from where I'm at here in Tokachi.
It looks like they have used Sportsentry in the past.
You can download the event PDF from their website.
Since this event is past already, I'll have to keep an eye out for the information for next year's event.