Yudomari Onsen is a small seaside hot spring on Yakushima's south coast, with simple outdoor pools set close to the rocks and the open water. The main bath is divided by a bamboo screen, and a smaller pool farther along the path gives a quieter soak.
It is best treated as a low-key coastal stop rather than a spa resort: bring your own towel, expect basic facilities, and leave time for a short walk down to the sea between baths.