Held every 7 years, it is designed to bring the people and local gods closer together. Although how belting down a hill on a log is supposed to achieve this I don’t know.
The overall aim (apart from avoiding serious injury) is to try and stay on the log all the way to the bottom of the hill. But by clicking on the picture below and watching the video, you can see it’s by no means easy.
Personally I like the way everyone jumps on at the end, just as the log has come to a standstill. But I’m not sure what the gods would make of such brazen cheating.