A sand bath is a type of Japanese bathing where you get buried in warm sand up to your neck while wearing yukata bathrobe. This is hard to do by yourself, so usually there is a person who uses a shovel to cover you in sand.
Being buried in warm sand helps the blood circulation and removes the toxic substance from your body. Some say that sand bathing was in practice as early as the edo period.
Surigahama onsen in Ibusuki spa is famous for being a spot on the kilometer long beach heated by geothermal hot spring.
It is said that a famous Japanese poet Akiko Yosano also visited Surigahama onsen. In some places on the nearby beach, you can enjoy swimming in the ocean and experience sand bath at the same time.