The saunatonttu (guardian of the sauna).

In 1909 Juho Tyyskä from Eräjärvi wrote down a denoscription of the saunatonttu, according to which the entity is black and one-eyed. Hence the popular saying "black like a saunatonttu".

The saunatonttu is a haltija (a spirit, gnome, or elf-like creature in Finnish mythology that guards, helps, or protects something or somebody) of the sauna. It protects the sauna and grants success to the owner and users of the sauna. If mistreated, the tonttu might burn down the sauna, break the sauna stove, or cause bitter fumes to come from the stove and fill the sauna.

Improper conduct angered the saunatonttu. Improper would be using the sauna too late at night or making loud noises. It was believed that blood might drip down from the sides of the roof, or cold water would suddenly boil if the saunatonttu got mad. Some also believed the being could assume the shape of an old woman and beat the sauna-goer to exhaustion with a vihta (sauna whisk).

The saunatonttu and its family lived in the sauna. When a new sauna was built, the tonttu had to be persuaded to move there.

In Olonets Karelia this would be done by uttering the following invocation:

"Ižandaized, Emagaižed, lähkad uudhe kylbetihe!"

(Master and mistress, come to the new sauna!)

The spirit under all its names in the Netherlands and Flanders