Consistently topping lists of the world's best onsen, Tamatebako is in two parts: conventional, ocean-view baths on a cliffside and a sunamushi (sand bath). Gender-separated baths are Japanese (more popular) or Western style and switch daily; on odd-numbered days men get the Japanese bath, with a view of Kaimon-dake. Sand-bath admission includes yukata; towels can be rented.
Nearby is the site of an old salt works where geysers stream water from the earth. Stand in the spray and it will taste like salt.
Tamatebako Onsen is a 9.5km drive from Ibusuki Station; follow signs for 'Healthy Land'.