A builder offered to raise the walls of Asgard in three seasons in exchange for Freyja, the sun, and the moon. Loki tricked the builder by transforming into a mare. Thor slew the builder once it was revealed he was a giant.
Þá er Æsir höfðu sett Miðgarð ok gert Valhöll þá kom þar smiðr nokkurr ok bauðst at gera þeim borg þá sem aldri myndi falla fyrir bergrisum eða hrímþursum. Hann mælti til kaups Freyju ok vildi hafa sól ok mána. Æsir gerðu sér ráð þetta við ráð Loka. Þeir mæltu honum til at hann skyldi þat vinna ok vera einn at verki ok gera þat á einum vetri.
After the gods had established Midgard and built Valholl, a builder came and offered to raise a fortress for them that would never fall to the mountain giants or frost giants. He asked for Freyja as payment and wanted the sun and moon besides. The gods took counsel and followed Loki's advice. They agreed to his terms on condition that he complete the work alone and within a single winter.
Loki brá sér í merylæti ok hljóp at Svaðilföra. En er jötunninn hljóp at merrinni þá gékk hann frá steininum ok Æsir náðu kaupinu. Þá tók Þórr hamarinn Mjölni ok lýkr af höfðið smið þeim er reyndist jötunn.
Loki transformed himself into a mare and ran toward Svadilfari. When the giant ran after the mare he left the stone, and the gods won the wager. Thor then raised the hammer Mjölnir and smashed the skull of the builder, who was revealed to be a giant.