The waterfalls of Norway · Water spirit
Fossegrim

"If you sit at the top of the waterfall, preferably on a bright moonly evening, then you will hear and see the waterfall spirit. Down below in the black cauldron, amid the rings of frothing foam, he sits playing Nature's powerful melodies. At first it is only a thundering roar, but little by little it will take hold of you so that you want to throw yourself down into the music's echoing stream…" (Theodor Kittelsen, Troldskab, 1892)
The raw, wild powers of the waterfall have stirred people's imagination for hundreds of years, and if you listen to the melodic sound of a roaring waterfall, it is easy to understand why people would get the impression of a strong, powerful being living in the waterfall, embodying this wild power. In Norway, this creature is known as fossegrim.
The Fossegrim, also known simply as "the Grim", is a water spirit or troll in Scandinavian folklore. He is described as an exceptionally talented fiddler: the sounds of forest, wind and water play over his fiddle strings. He usually appears as either a grim, crooked old man, thus the name ("grim" is an old Scandinavian word meaning "ugly") or a handsome young man, but is usually naked (with the rare exception of a tiny loincloth) due to his wet surroundings. The fossegrim is known to occasionally fall in love with a young woman or man and to use his music to enchant them to come join him in the waterfall. He learns too late, however, that humans cannot breathe underwater and are bound to drown, leaving him more lonesome than ever.
The fossegrim can be enticed to teach his incredible skill with the fiddle. You must visit the waterfall with a fiddle for three Thursdays in a row, during the evenings. On the first two Thursdays you would need to throw a treat into the waterfall - preferably a stolen piece of ham or cheese. Then, on the third night, if the offering was generous and the fossegrim liked it, he will grab your bowing hand and guide it until your fingers bleed. After this, you will be able to play as well as the fossegrim himself. But remember, whenever you visit the fossegrim for playing lessons, his power over you grows, so make sure to end the lessons in time lest you become a mindless slave to his will…