Hot Springs are resting spots where Jin bathes to permanently raise his maximum health. There are 18 on Tsushima and 2 more on Iki Island, and soaking in all 18 Tsushima springs unlocks the Fundoshi.
Walk into the water and rest. Jin then reflects on one of two topics picked at random from a pool, such as his mother, his uncle or an ally. More topics open up as you finish tales.
They are worth an early detour, since the health boosts stack and make every fight easier. Many sit near story locations, so check the map as you travel.
Shinto Shrines
Shinto Shrines are climbing challenges marked by torii gates, each ending at a summit shrine that rewards a major charm. Ghost of Tsushima has 17 of them: 16 on Tsushima and one on Iki Island.
Castle Kaneda
Castle Kaneda is the Izuhara castle where Khotun Khan holds Lord Shimura prisoner after the Battle of Komoda Beach. You storm it with your allies in Shadow of the Samurai to free your uncle and end Act 1.
Kushi Temple
Kushi Temple, also known as Kushidera, is an old pagoda that has stood in Toyotama for centuries. It is a key stop in Norio's storyline. Its monks later fight at the siege of Castle Shimura.
Maple Shade Hot Spring
Maple Shade Hot Spring sits in Kubara, part of Toyotama, and is one of the game's 20 Hot Springs. Soak there once and Jin's maximum health goes up permanently.