A Hot Spring is the most common way to heal in the game Mother 3. Anybody can use it. There are many of them throughout the Nowhere Islands, but are mostly located in long dungeons or right before bosses. They will restore the party to full HP and PP.
If you listen carefully the music playing is a slow version of the music playing during the Osohe Dance.
The Hot Springs only appear in Mother 3 and Mother 2, although there is only one Hot Spring in Mother 2. Other games use different ways of resting. There is usually one Hot Spring in each dungeon, and about 4 in each Chapter. One that is weird, and one that Boney will not go into is the Hot Spring of Tane Tane Island, after eating the Tane Tane Shrooms. This probably means that dogs are impervious to illusions. For some strange reason, this one does heal you. Maybe you only think you're healed...but that Hot Spring is really a junk heap. The real Hot Spring is in the door behind it.
In Chapter 8, below New Pork City, there is a Hot Spring in a box, which still acts as a Hot Spring. Later in the area, there is a green Hot Spring, yet it is still a hot spring. This proves that there are many different variations of the Hot Spring, but all of them are helpful when it comes to advancing in the storyline.
Well, the Hot Springs are mainly used for healing HP and PP, but they are also used for healing any type of status effect. And, they can change graphics. When you walk into one at the beginning of the game while Flint and Fuel are burned, the area below their neck will revert back to their original look, so that it is half burned half original.