Flew from Osaka to Beppu in Kyushu on my way to Yufuin hot spring resort last December. Spent 1 night there which was enough to see all the major interesting sights. Did not have enough time to do the hot sand bath though lol-
Probably doesn't feel that much different if buried on a hot beach. A colorful umbrella probably a good idea too so won't get run over by a beach cleaning truck 馃槀