At minimum, the sauna mechanic requires:
sauna stove; an ordinary fireplace isn't adequate for the purpose
- Most villages will have a sauna building with the stove, a tub to hold water, and a bench (this piece of furniture is just there for immersion afaik)
- If you wish to have your own stove, you must 1) have a fully constructed wooden building with the walls and floors done; 2) gather 40 stones + 15 rocks to construct the stove.
A sauna building may also function as a smokehouse, or a small starter home before you acquire the materials for a bigger living space.
fuel to heat the stove for several hours: a good steam requires about 50 pounds of fuel (equivalent to 1 slender tree trunk)
water for steam
- Pick up a container (any size will do)
- Stand next to a water source and open the inventory
- Use the [a] apply key and select the container you wish to fill
- Stand next to the sauna stove and open the inventory
- Use the [a] apply key and select the container with water
- The message log will inform you about the status of the stove's steam; you'll also see the screen flash white and hear sound effects of water being thrown on the heated sauna stove
In general terms for the game's setting, when the weather is freezing a sauna bath becomes the main method of maintaining hygiene. Although hygiene as a system isn't modeled in the game, using the sauna gives a boost to the player's health in terms of wound/illness recovery rate. (For symptoms of poisoning, you're basically sweating out the toxins.)
Applying a vasta will buff the health benefits, so it's a good idea to stock up on birch twigs when they're in season during the summer.
Since the game performs checks to wound status once a day in the morning, a daily sauna regime could help when you require it.