The Water-Nix by The Brothers Grimm
A little brother and sister were once playing by a well, and while they were thus playing, they both fell in. A water-nix lived down below, who said, “Now I have got you, now you shall work hard for me!” and carried them off with her. She gave the girl dirty tangled flax to spin, and she had to fetch water in a bucket with a hole in it, and the boy had to hew down a tree with a blunt axe, and they got nothing to eat but dumplings as hard as stones. Then at last the children became so impatient, that they waited until one Sunday, when the nix was at church, and ran away. But when church was over, the nix saw that the birds were flown, and followed them with great strides. The children saw her from afar, and the girl threw a brush behind her which formed an immense hill of bristles, with thousands and thousands of spikes, over which the nix was forced to scramble with great difficulty; at last, however, she got over. When the children saw this, the boy threw behind him a comb which made a great hill of combs with a thousand times a thousand teeth, but the nix managed to keep herself steady on them, and at last crossed over that. Then the girl threw behind her a looking-glass which formed a hill of mirrors, and was so slippery that it was impossible for the nix to cross it. Then she thought, “I will go home quickly and fetch my axe, and cut the hill of glass in half.” Long before she returned, however, and had hewn through the glass, the children had escaped to a great distance, and the water-nix was obliged to betake herself to her well again.